The <map> element

Categories:

Flow content.

Phrasing content.

Palpable content.

Embedded content.

If the element has a controls attribute: Interactive content.

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

If lat, lon, and zoom are NOT present: Transparent; otherwise: Zero or more layer or area elements.

Content attributes:

Global attributes.

zoom — A positive integer zoom (scale) value.

lat — A decimal WGS84 latitude value for the map center.

lon — A decimal WGS84 longitude value for the map center.

projection — A case-sensitive string identifier of the MapML coordinate reference system used by the map. Default is OSMTILE.

controls — Show user agent controls.

controlslist — Show/hide specific user agent controls.

width — Horizontal dimension.

height — Vertical dimension.

Tag omission in text/html:

Neither tag is omissible.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
role=map	role: application Global aria-* attributes and any aria-* attributes applicable to the allowed roles and implied role (if any).

For implementers

DOM interface:

          [Exposed=Window, LegacyFactoryFunction=Map(unsigned long width, unsigned long height, double lat, double lon, unsigned short zoom, optional DOMString projection, boolean controls)]
          interface HTMLMapElement : HTMLElement {
            [HTMLConstructor] constructor();
            
            [SameObject] readonly attribute HTMLCollection areas;
            [CEReactions] attribute unsigned short zoom;
            [CEReactions] attribute double lat;
            [CEReactions] attribute double lon;
            readonly attribute DOMString projection;
            [CEReactions] attribute boolean controls;
            [SameObject, PutForwards=value] readonly attribute
                DOMTokenList controlsList;
            [CEReactions] attribute unsigned long width;
            [CEReactions] attribute unsigned long height;
            undefined zoomTo(double latitude, double longitude, optional unsigned short zoom);
          };
          

The <layer> element

Categories:

None.

Contexts in which this element can be used:

As a child of the map element.

Content model:

If the src attribute is present: Nothing. If no src attribute is present: Metadata content describing nested Map Markup Language content.

Content attributes:

Global attributes.

src — Address of the resource.

label — String label for the layer in the layer control, if displayed.

checked — Layer on/off status.

disabled — Sets the disabled state of the layer in the layer control.

hidden — Visibility status of the layer in the layer control.

referrerpolicy — Referrer policy for fetches initiated by the element.

crossorigin — A CORS settings attribute, specifies how the element handles crossorigin requests.

Tag omission in text/html:

Neither tag is omissible.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

          [Exposed=Window]
          interface HTMLLayerElement : HTMLElement {
            [HTMLConstructor] constructor();
            
            readonly attribute DOMString src;
                     attribute DOMString label;
                     attribute boolean checked;
            readonly attribute boolean disabled;
                     attribute boolean hidden;
                     attribute DOMString referrerPolicy;
                     attribute DOMString? crossOrigin;
                               undefined zoomTo();
          };
          

The map element displays its child layer elements similarly to "acetate" layers on a (paper) map. The layers follow the painters model, whereby layer elements are displayed on top of earlier siblings according to their document order. layer transparency is controlled by the CSS opacity property. [[SVG2]] [[css-color-3]]

In contrast to the HTML media elements' source child element where a single source element is selected by the user agent for play, the map element's child layer elements are visually combined with sibling layer elements and presented by the parent map element as a pan-able, zoom-able two-dimensional image. The display state (on / off) of the content represented by the layer element is controlled by the checked boolean attribute and corresponding property. If checked, the layer is drawn on the map in the sequence it is found in the parent element; if not checked the layer is not drawn but should remain visible in the map element's representation of controls in an "unchecked" state.

The src attribute value is the URL of a web resource encoded in Map Markup Language.

The hidden boolean attribute can be set to remove the layer from the map layer control, but it will remain displayed on the map. In order to remove the layer from the map display, it can have its checked property toggled, or be removed from the DOM.

The disabled property is a read-only boolean indicator of the visibility of the layer on the map. If the layer is not visible due to errors, including projection, zoom or extent mismatch, the property will be true and if the layer is present in the layer control (i.e. hidden is false), it will be disabled in that control i.e. not checkable.

The location and zoom level of the map can be changed via the layer.zoomTo() API method.

The <area> element

Categories:

Flow content.

Phrasing content.

Contexts in which this element can be used:

As a child of the map element.

Content model:

Nothing.

Content attributes:

Global attributes.

href — Address of the hyperlink.

alt — User-visible label.

coords — Coordinates for the shape to be created on the map.

shape — The kind of shape to be created on the map.

Tag omission in text/html:

Neither tag is omissible.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
area with href: role=link	No role Global aria-* attributes and any aria-* attributes applicable to the allowed roles and implied role (if any).
area without href: No corresponding role	No role Global aria-* attributes and any aria-* attributes applicable to the allowed roles and implied role (if any).

For implementers

DOM interface:

          [Exposed=Window]
          interface HTMLAreaElement : HTMLElement {
            [HTMLConstructor] constructor();
            
            attribute DOMString href;
            attribute DOMString alt;
            attribute DOMString coords;
            attribute DOMString shape;
          };
          

The area element allows the HTML author to encode and style a limited set of spatial feature types on its parent map element, using familiar [[HTML]] image map coordinates. Such features can be optionally designated as hyperlinks to be selected by the user.

If present, the href attribute identifies the designated coordinate area as a hyperlink. If no href attribute exists, the area is designated as a non-interactive area. The alt attribute specifies a label which can be used by the user agent for ephemeral and non-visual labelling of the area.

If the area element has no href attribute, then the area represented by the element cannot be selected, and the alt attribute must be omitted.

The coords attribute is a comma-separated list of integer coordinate values which delimit the geometry of the (area) feature. The shape attribute identifies the type of geometry which is encoded as coordinates in the coords attribute.

The shape attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map.

The shape attribute may be omitted. The missing value default is the rectangle state.

The coords attribute must, if specified, contain a valid list of integers. This attribute gives the coordinates for the shape described by the shape attribute. The processing for this attribute is described as part of the image map processing model.

In the circle state, area elements must have a coords attribute present, with three integers, the last of which must be non-negative. The first integer must be the distance in CSS pixels from the left edge of the image to the center of the circle, the second integer must be the distance in CSS pixels from the top edge of the image to the center of the circle, and the third integer must be the radius of the circle, again in CSS pixels.

In the default state, area elements must not have a coords attribute. (The area is the whole area of the map on the page.)

In the polygon state, area elements must have a coords attribute with at least six integers, and the number of integers must be even. Each pair of integers must represent a coordinate given as the distances from the left and the top of the map in CSS pixels respectively, and all the coordinates together must represent the points of the polygon, in order.

In the rectangle state, area elements must have a coords attribute with exactly four integers, the first of which must be less than the third, and the second of which must be less than the fourth. The four values must represent, respectively, the distance from the left edge of the map to the left side of the rectangle, the distance from the top edge to the top side, the distance from the left edge to the right side, and the distance from the top edge to the bottom side, all in CSS pixels.

The intention of the area element is to extend the behavior of the existing [[HTML]] area element. For information pertaining to the processing of various link types created by the area element, please refer to the description of hyperlink processing for the [[HTML]] area element.

Coordinate Systems

In this document, all Coordinate Systems (CS) are 2D. A 2D CS has two axes, one horizontal (commonly related to west-east direction), and one vertical (commonly related to north-south direction; do not confuse it with "elevation"). This document defines the axis order of coordinate pairs serialized in MapML documents which the axis-specific values are not distinguished by markup, such as within the coordinates element. In documents conforming to this specification, we override any externally defined axis order. Coordinates are serialized as horizontal axis followed by vertical axis, separated by whitespace. Where applicable, coordinate pairs are separated by whitespace. The axis names of a coordinate system are identified by this document.

Coordinate Reference Systems

A Coordinate Reference System (CRS) is a Coordinate System that is referenced to locations on the Earth. Maps are graphics which follow mathematical rules (called projections) established to transform locations on Earth to locations on a plane (formerly paper, more recently a device screen). Projections are mathematical equations designed to conserve particular properties of the source location, and often have parameters that can be used to induce desired properties for particular locations.

To facilitate the sharing of CRS definitions, the International Association of Oil ans Gas Producers (IOGP) (formerly known as the European Petroleum Survey Group (EPSG)) mantains a list of CRS definitions and codes in their [[[EPSG-REGISTRY]]]. Some EPSG codes are used in the following table. In an effort to bring some clarity about the axis order for the longitude-latitude based CRSs, the OGC defined some "CRS codes". CRS:83 is defined equivalent to EPSG:4269 but with horizontal-then-vertical axis order, and CRS:84 is defined equivalent to EPSG:4326 except in its axes order. [[EPSG-REGISTRY]]

Tiled Coordinate Reference Systems

A Tiled Coordinate Reference System is a set of Coordinate Reference Systems, which share a common origin in space, but which differ by the size of their smallest unit at defined locations, e.g. meters/pixel along the equator.

This document defines the following coordinate reference system types:

MapML documents are similar to other spatial information with regard to definition of projection and coordinate system requirements. However, MapML defines a system of communicating coordinate system information across the uniform interface of HTTP in order to eliminate assumptions in shared coordinate systems: the coordinate systems requested by the client and available from the server are represented as simple defined string identifiers defined in the table below, and exchanged in markup defined by this specification.

* All coordinate reference systems' coordinate pairs, where not explicitly marked up or identified by axis (for example, in the coordinates element) are defined by this specification to be in "horizontal axis followed by vertical axis" order. Where axes order is defined differently by external definition, this specification MUST be taken to be correct for MapML documents.

OSMTILE

This specification defines the string "OSMTILE" to be the identifier of a tiled coordinate reference system projected (in the Web Mercator system) and scaled into 19 zoom levels (0-18) at defined resolutions. The OSMTILE coordinate reference system has become a de facto interoperable standard for 'slippy' Web maps. The OSMTILE coordinate reference system is suitable for small scale mapping of the Earth, exclusive of north and south polar latitudes, where distortion is extreme.

Some of the major defining characteristics of the OSMTILE coordinate reference system include the fact that a large portion of the surface of the earth is represented by a single 256px by 256px tile (image) at zoom level 0, with successive zoom levels' tiles dividing the area represented by the parent tile into four equal quadrants, and 'nesting' perfectly within the parent tile such that each successive level of tiles contains 2 ^zoom individual tiles. The geo-registration of tiles at all zoom levels is defined by the coordinate system definition, and they can thus be 'mashed up' with other spatial data in a defined manner.

CBMTILE

The "CBMTILE" tiled coordinate reference system is suitable for small to medium scale mapping of Canada.

APSTILE

The "APSTILE" tiled coordinate reference system is based on the Stereographic family of map projections, with the North polar aspect, per the EPSG::5936 coordinate reference system. This projection system is suitable for displaying areas in (north) polar latitudes.

WGS84

This specification defines the string "WGS84" to be the identifier of a tiled coordinate reference system projected in the Equirectangular, or Plate carrée system.

The WGS84 tiled coordinate reference system is suitable for small to medium scale mapping of the entire world. It is also useful for vector data provided that the inter-vertex distance is no less than a single pixel in size at any particular zoom level.

It is believed that the definition of WGS84 according to this document makes it a suitable choice for non-georeferenced mapping applications, such as ultra high resolution graphics and technical drawings are one of the their use cases. The editor of this document requests specific implementations to contribute implementation experience in using this TCRS for technical and other drawings.

Other coordinate reference systems

Many other projection systems exist, and could in principle be used by map clients and servers. As such projections and associated defined tiled coordinate reference systems come into common usage, it is expected that their definitions for use in MapML and on the Web will be imported here. The contents of this document constitutes a registry of such projections.

Scale / Resolution / Zoom levels

Scale is an essential characteristic of all geospatial information. The scale at which information is used dictates the model used for its representation. Geospatial information cannot be meaningfully combined without consideration given to its scale. Entire cities are represented on 'small scale' maps as dots, whereas on another large scale map, a single city could have many thousands of individual features in its depiction.

Not only is scale important in the portrayal of maps, it is also essential when defining the model of underlying feature data.

Map projections distort the surface of the earth in ways which suit the objectives of the projection definition. As a result of that distortion, the scale and the resolution of maps in that projection vary as a function of location. The resolutions specified by this document are only valid in defined locations. For example, in WGS84 and OSMTILE the defined resolutions are valid only along the equator. "Zoom" levels are integer values corresponding to the index of the resolution value defined above, and represent numeric proxy for a scale, at the defined location(s). For example, the OSMTILE TCRS, being based internally on the Spherical Web Mercator projection (EPSG::3857), allows us to reasonably portray a large portion of the Earth's surface, requiring relatively simple and fast math to convert to and from spherical latitude/longitude coordinates. Additionally, it enables the simple tiling system known as OSMTILE in this specification, that has become a de facto standard. As such, it was deemed to have appropriate properties for a globally useful projection on the Web.

In MapML documents, scale is indirectly represented by zoom level, and varies across any rendered map extent. Two MapML documents in the same TCRS and zoom level should be interoperable to the degree that they can be automatically and visually related (overlayed). The zoom level of a MapML document is often represented by the value of the value attribute of the input[@type=zoom]. By associating a specific zoom value to the input, we are able to compute the spatial bounds of a link template by means of min, max and axis values of other input[@type=location] elements associated to the same link template element with which the input[@type=zoom] is associated. In any case, the zoom level of any MapML document MAY be present in document metadata as a meta element e.g. <meta name="zoom" content="0"/>. In the case where a MapML document contains an extent element, an input@type=zoom MUST be present which controls how the zoom is transmitted from client to server. Where that input has a non-empty input@value attribute, in case of discrepancy between the meta[@name=zoom]/@content and the input[@type=zoom]/@value, the latter zoom value SHALL be taken to be correct, EXCEPT in the case where there may exist more than one input[@type=zoom] and their value attributes do not agree, in which case the value of meta[@name=zoom]/@content shall be taken to be correct.

Extents

A MapML document is a representation of a defined portion of a two dimensional map area. In MapML, this is called an 'extent' (represented by the extent element), the extremes of which can be described in terms of locations coordinates specified in the TCRS (pcrs, gcrs, tilematrix, etc.). The extent/@units value SHALL be taken to be the authoritative declaration of the TCRS for a MapML document.

Fragment identifiers

TBD

The Document object

A MapML document is an XML document, with all elements assigned to the HTML namespace. As such, a MapML document MUST have a single root element named mapml , generally having a single attribute named "xmlns" with a value which MUST be equal to "http://www.w3.org/1999/xhtml". Assigning elements to namespaces using namepace prefixes is NOT recommended. At this time, there is only an XML syntax variety of MapML document, and documents conforming to this specification MUST NOT have a DOCTYPE declaration.

The <mapml> element

Categories:

None.

Contexts in which this element can be used:

The root of a MapML document.

Content model:

One head element, followed by one body element.

Content attributes:

Global attributes.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLMapmlElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

The mapml element is the the root element of a MapML document, and must contain one head element followed by one body element.

The mapml element may carry a lang attribute, as defined by [[HTML]].

The <head> element

Categories:

None.

Contexts in which this element can be used:

As the first child element of the mapml element.

Content model:

One or more elements of metadata content, of which exactly one is a title element and no more than one is a base element.

Content attributes:

Global attributes.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLHeadElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

The head element is for MapML document metadata content. The content may include: one title element, one base element, zero or more link elements, and zero or more meta elements.

The <title> element

Categories:

Metadata content.

Contexts in which this element can be used:

As a child of the head element.

Content model:

Text that is not inter-element whitespace.

Content attributes:

Global attributes.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLTitleElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
          

The title element should exist as the one and only title element in the head element. Its content should be a text string describing the document. It is conceivably used as a bookmark title.

The <base> element

Categories:

Metadata content.

Contexts in which this element can be used:

As a child element of the head element.

Content model:

Nothing.

Content attributes:

href — The absolute URL to be used to resolve relative URLs in the document.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLBaseElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

The base element is used to identify a URL to be used to act as a base URL in order to resolve relative URLs later in the document.

There must be only one base element in a MapML document, and it must be in the content of the head element, before any MapML elements which potentially carry a URL for resolution, notably the link element.

The <meta> element

Categories:

Metadata content.

Contexts in which this element can be used:

In the head element.

Content model:

Nothing.

Content attributes:

name — Metadata name.

http-equiv — Pragma directive.

content — Value of the element.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLMetaElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString name;
              attribute DOMString httpEquiv;
              attribute DOMString content;
            };
            

The <link> element

Categories:

Metadata content.

Contexts in which this element can be used:

If the element represents a hyperlink (has a href attribute): as a child of the head or body element.

If the element represents a link template (has a tref attribute): as a child of the extent element.

Content model:

Nothing.

Content attributes:

href — Address of the hyperlink.

tref — URL Template.

rel — Relationship between the document containing the element and the destination resource.

projection — The TCRS of the linked resource.

hreflang — Language of the linked resource.

type — Hint for the type of the referenced resource.

title — Title of the link.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLLinkElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString href;
              attribute DOMString tref;
              attribute DOMString rel;
              attribute DOMString projection;
              attribute DOMString hreflang;
              attribute DOMString type;
              attribute DOMString title;
            };
          

The link element allows authors to link their document to other resources.

The destination of the link(s) is given by the href attribute, which must be present and must contain a valid non-empty URL potentially surrounded by spaces. If the href attribute is absent, then the element does not define a link.

A link element must have a rel attribute. If the rel attribute is absent, then the element does not define a link.

The types of link are given by the value of the rel attribute, which generally has a value that is a single token, except in the case of the link@rel='self style' value described below. The allowed keywords and their meanings are defined below. If the rel attribute is absent, has no keywords, or if none of the keywords used are allowed according to the definitions in this specification, then the element does not create any links.

The projection attribute value identifies the TCRS of the linked resource, with a value from the defined set of TCRS identifiers. When rel=alternate is used together with the projection attribute, clients may be able to perform agent-driven content negotiation to provide a better user experience. For example, if an HTML author mistakenly enters the URL of an OSMTILE resource in their HTML layer@src attribute, but the map in which the layer takes part is declared to be CBMTILE, the MapML author can ease the potential for resultant confusion by providing appropriate rel=alternate links to equivalent MapML resources in other projections.

The link/@title value can be used in conjunction with link[@rel=license] as a string description of the link to the terms under which the MapML content is made available, while the link/@href value is used to link to an HTML document of the license terms. Note that there may be more than a single contributor to the information presented in a single extent, and it is therefore possible to have several licenses terms for a single extent, each of which will have its own link element in a single MapML document.

The link@rel='self style' rel value can be used to designate one of a set of alternative named style links as being the style of the current document. As such, the value of the link@title attribute will be used by the user agent to label the current style from among the list of alternate styles.

The link[@tref] element represents a URL template for a resource (e.g. tiles) which can be used by the client make requests for resources to fill its extent at zoom levels and bounds indicated by sibling input[/@type=location] elements' min and max attributes, or to (partially) identify URL targets suitable to enable query of server resources. The rel attribute contains a keyword string which identifies the role of the resource(s) for which the tref attribute value represents a URL template, which may contain zero or more input/@name variable references. Such variable references must be a case-insensitive match of sibling input elements' name attribute.

The content represented by link[@tref] elements should be painted in document order of the appearance of the link[@tref] elements.

The <body> element

Categories:

Sectioning root.

Contexts in which this element can be used:

As the second child of the mapml element.

Content model:

Features and metadata.

Content attributes:

Global attributes.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
role=document	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLBodyElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

The body element represents the content of the document.

The <extent> element

Categories:

Metadata content.

Contexts in which this element can be used:

Required to be a child of the body element.

Content model:

A set of multiple input and one or more link elements with their rel attribute in either the "tile", "image" or "features" state, and zero or one link element with its rel attribute in the "query" state.

Content attributes:

units — The name of the coordinate reference system whose measurement units are to be used by values submitted by child input elements.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLExtentElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString units;
              readonly attribute long length;
              getter Element (unsigned long index);
              getter (RadioNodeList or Element) (DOMString name);
            };
            

The extent element is a map-associated affordance, which contains input and link elements, whose job it is to serialize location event properties that can be submitted to a server for processing.

The units attribute indicates the parent TCRS that location events shall be generated for, and serialized as requested by the extent's contents.

The <input> element

Categories:

N/A.

Contexts in which this element can be used:

Required to be a child of the extent element.

Content model:

Nothing.

Content attributes:

type — Enumerated keyword string identifies the type of input.

name — The token to be used as a variable name in form serialization.

value — The current or default value of the name/value pair represented by the input.

min — The minimum value for the extent parameter acceptable by the server.

max — The maximum value for the extent parameter acceptable by the server.

step — The increment by which a value may vary between the min and max values.

units — When type attribute is location, enumerated keyword string identifies the associated coordinate system for this input.

axis — When type attribute is location, enumerated keyword string identifies the axis of the associated OR related coordinate system from the units attribute, for which an associated axis value will be returned. The min and max attribute values, if present, will be interpreted in the defined units of this axis.

rel — When type attribute is location, tile or image (the default if not specified) identifies the relation of this location to either a tile or an image corresponding to the map extent in which the location is found. Establishes the meaning of the position attribute to identify the location relative to the tile in question or to the map extent (the default).

position — When type attribute is location, enumerated keyword string identifies the relative position of a location.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
input with type: zoom location width height hidden No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLInputElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString type;
              attribute DOMString name;
              attribute DOMString min;
              attribute DOMString max;
              attribute DOMString step;
              attribute DOMString units;
              attribute DOMString axis;
              attribute DOMString rel;
              attribute DOMString position;
              attribute DOMString value;
            };
            

The input element represents a typed data field, associated with a map extent form, to allow the user agent to request documents for a specific map area.

The type attribute controls the data type (and associated control) of the element. It is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states in the cell in the second column on the same row as the keyword.

When the type attribute is in the "location" state, the input may have three associated attributes: units, axis and position. units identifies the associated coordinate system that the location is referred to. Each Tiled Coordinate Reference System (TCRS) instance may have one or more associated coordinate systems that are coordinate reference system by virtue of their defined association to the TCRS. For instance, the OSMTILE TCRS is associated to the underlying coordinate reference system known commonly as Web Mercator, by virtue of an origin location, defined in meters in the EPSG:3857 CRS plus a set of zoom level resolutions, and a transformation.

The meaning of the position attribute value (keyword) depends upon the presence and value of the associated rel attribute. When the rel attribute is not present or has the value image, the position attribute keyword value describes the input location relative to the ancestor extent. When rel=tile (only applicable when the units value equals tilematrix), the position attribute values describe the input location relative to the tile at the location in question.

The axis keyword identifies the axis of the coordinate that the input variable represents. The coordinate system should be identified by the units attribute.

The <label> element

Categories:

N/A.

Contexts in which this element can be used:

As a child of the extent element.

Content model:

Phrasing content.

Content attributes:

for — Identifies by id reference the select for which the content of this element is the label.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLLabelElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString for;
            };
            

The <select> element

Categories:

N/A.

Contexts in which this element can be used:

As a child of the extent element.

Content model:

One or more option elements.

Content attributes:

id — Identifies the select within the current document.

name — The token to be used as a variable name in form serialization.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLSelectElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString id;
              attribute DOMString name;
            };
            

The <option> element

Categories:

N/A.

Contexts in which this element can be used:

As a child of the select element.

Content model:

Nothing.

Content attributes:

value — The value to be used in form submission.

label — The label to be presented to the user, if applicable.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLOptionElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString value;
              attribute DOMString label;
            };
            

The <tile> element

Categories:

Feature data.

Contexts in which this element can be used:

Child of the body element.

Content model:

Nothing.

Content attributes:

row — An integer (a Y axis value / the tile size) in the range of the tile coordinate reference system.

col — An integer (a X axis value / the tile size) in the domain of the tile coordinate reference system.

src — A URL from which the tile may be obtained.

type — A hint about the MIME type of the resource obtainable at the src URL.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLTileElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute long row;
              attribute long col;
              attribute DOMString src;
              attribute DOMString type;
            };
            

The tile element is a type of feature which is associated with a tiled coordinate reference system that subdivides or 'tiles' 2D space in a recursively repeating grid pattern, where the origin of both the tiled coordinate reference system and the grid at all zoom levels is defined in coordinates of an underlying projected coordinate reference system.

A defining characteristic of tiled coordinate reference systems is that they rely on integer grid row/col coordinates and zoom values. The use of these values in URLs can yield highly cacheable resources, which can lead to high-performance map services.

The "zoom" value is a global integer property of a MapML document whose coordinate system is defined by this specification. All MapML documents have a defined zoom value. The "zoom" value is equal to the zoom@value child of the extent element. Hence the zoom value is not a direct attribute of the tile element.

The main example of such a tiled coordinate reference system is OSMTILE, although others exist.

The <image> element

Categories:

Feature data.

Contexts in which this element can be used:

A child of the feature element, which has a sibling bbox element.

Content model:

Nothing.

Content attributes:

src — Address of the hyperlink.

type — A hint as to the MIME type of the resource.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLImageElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

The <feature> element

Categories:

Feature data.

Interactive content.

Contexts in which this element can be used:

Child of the body element.

Content model:

Optional featurecaption element, optional geometry element, optional properties element, optional image element.

Content attributes:

Global attributes.

zoom — the 'native' zoom level of the feature geometry.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
role=feature	No role Global aria-* attributes and any aria-* attributes applicable to the allowed roles and implied role (if any).

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLFeatureElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              attribute DOMString zoom;
            };
            

A feature element represents a map feature.

The <featurecaption> element

Categories:

Feature data.

Contexts in which this element can be used:

As a child of a feature element containing no other featurecaption elements.

Content model:

Text that is not inter-element whitespace.

Content attributes:

Global attributes.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLFeaturecaptionElement : HTMLElement {
              [HTMLConstructor] constructor();
              
            };
            

The featurecaption element represents a caption for the contents of the featurecaption element's parent feature element.

The <properties> element

Categories:

Feature data.

Contexts in which this element can be used:

A child of the feature element.

Content model:

Palpable content

Content attributes:

N/A.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLPropertiesElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

The <geometry> element

Categories:

Feature data.

Contexts in which this element can be used:

Child of the feature element.

Content model:

A single geometry value, described in the table below.

Content attributes:

Global attributes.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLGeometryElement : HTMLElement {
              [HTMLConstructor] constructor();
              
              readonly attribute DOMString type;
            };
            

A geometry element has one child element, which can be a point, linestring, polygon, multipoint, multilinestring, multipolygon, or geometrycollection.

The <coordinates> element

Categories:

Feature data.

Contexts in which this element can be used:

A descendant of the geometry element, as the coordinate data which defines a feature geometry.

Content model:

One or more positions in x followed by y, separated by whitespace, with each position separated from the adjacent position by whitespace.

Content attributes:

N/A.

Accessibility considerations:

For authors

Implicit ARIA semantics	ARIA roles, states and properties which MAY be used
No corresponding role	No role or aria-* attributes.

For implementers

DOM interface:

            [Exposed=Window]
            interface HTMLCoordinatesElement : HTMLElement {
              [HTMLConstructor] constructor();
            };
            

In MapML, features have positions in 2D space. A position is sometimes marked up with coordinate data explicitly identified by axis, for example in the tile element, the attributes row and col are used. Equally common is coordinate data which omits explicit markup of positions' axes, for example in the coordinates element. In the coordinates element, positions must be encoded in x,y order, separated by whitespace. The coordinates element is used to model the content of various geometries in MapML. Its content and the meaning of its content it depends on what geometry value it is used in. The context and content of the coordinates element is described in the geometry element table. A RelaxNG schema for MapML is provided below, however schema validation is not able to fully validate the context and content of the coordinates element. Such requirements are listed under the column "Non-schema constraints"

The positions in the coordinates element define the location of the feature. For geometry elements whose value is linestring, multipoint or multilinestring, this specification neither assigns nor requires special ordering or other constraints, apart from the axis order described above. For geometry elements whose value is a polygon or multipolygon element, the descendant coordinates elements must follow additional constraints.