| name | mapml-extent-markup |
| description | Tells you how to correctly create and edit the markup for a <map-extent> element. Use it when generating MapML output markup in an HTML page. |
The <map-extent> element is a hypertext control that is associated to and represents the
rectangle of the map viewport, from the user's perspective. Map authors use it
to compose server requests for layer content. Requests are composed using
URL templates processed by the browser as the map moves and requires new content
to paint. The URL templates each contain one or more variable references, with each
variable reference denoted by the name of the variable enclosed in braces {}.
Variables are created by the map author using the <map-input> element. There are
several types of <map-input>, allowing the map author to reference the corners
of the extent, its width and height, and its zoom.
An example of a <map-extent> element being used to load image tiles for a single
URL template.
<mapml-viewer projection="OSMTILE" lat="10" lon="0" zoom="1">
<map-layer label="OpenStreetMap" checked>
<map-extent units="OSMTILE" checked hidden>
<map-input name="z" type="zoom" value="18" min="0" max="18"></map-input>
<map-input name="x" type="location" units="tilematrix" axis="column" min="0" max="262144"></map-input>
<map-input name="y" type="location" units="tilematrix" axis="row" min="0" max="262144"></map-input>
<map-link rel="tile" tref="https://tile.openstreetmap.org/{z}/{x}/{y}.png"></map-link>
</map-extent>
</map-layer>
</mapml-viewer>
Attributes
units
Specifies the projection of the tiles and other content that is expected from the
server. If the projection value is a case-insensitive match of the <mapml-viewer>
projection attribute, the extent will be disabled in the layer control, and will
not be displayed on the map, nor content fetched.
Defined values of units include:
| Projection | Description |
|---|
| OSMTILE | Web Mercator, with 256px x 256px tiles recursively defined inside a square bounds at zoom = 0 |
| WGS84 | Pseudo plate carrée, with 256px x 256px tiles. Zoom = 0 contains two tiles in two columns, with their origin at -180,90. False easting and northing (pcrs) values inside the projection bounds correspond to longitude and latitude, respectively. |
| CBMTILE | Lambert Conformal Conic, with 256px x 256px tiles. Zoom levels chosen by scale denominator, so tiles do not nest. |
Author-defined values of units are possible, using the Custom projections API
The units attribute is required and can't be changed.
label
Specifies a label for an extent which is displayed in the layer control. When a label value is not provided, the label value defaults to 'Sub-Layer' in the layer control.
checked
The checked attribute and property is boolean. When present, the checked property value is taken to be 'true'; when not present, the property value is 'false'. The map-extent content will be fetched and rendered according to the checked state. Beware that it is the presence of the attribute that makes it true, not the value of the attribute. For example, the attribute checked="false" actually turns out to be checked, as described by MDN Web docs.
hidden
The hidden attribute and property is boolean. When present, the extent is hidden (not present) in the layer control. Regardless of hidden state, the layer is rendered or not depending on the checked attribute state.
opacity
The opacity attribute is used to set the initial opacity of the <map-extent> element.
Valid opacity values range from from "0.0" to "1.0" with strictly one demical place and are reflected in the extent settings
opacity input slider control. When the opacity attribute is not present, the opacity is set to "1.0" by default.
Examples
Multiple Extent
The following example shows multiple <map-extent> elements in a layer. The different elements can be selected from the three dots menu of the Basemap layer.
<mapml-viewer projection="OSMTILE" zoom="2" lat="53.331" lon="-91.667" controls>
<map-layer label="Basemap" checked="">
<map-extent units="OSMTILE" checked>
<map-input name="TileMatrix" type="zoom" value="18" min="0" max="18"></map-input>
<map-input name="TileCol" type="location" units="tilematrix" axis="column" min="0" max="262144"></map-input>
<map-input name="TileRow" type="location" units="tilematrix" axis="row" min="0" max="262144"></map-input>
<map-link rel="tile" tref="https://server.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer/WMTS/tile/1.0.0/World_Imagery/default/default028mm/{TileMatrix}/{TileRow}/{TileCol}.jpg"></map-link>
</map-extent>
<map-extent label="Nat Geo" units="OSMTILE" checked>
<map-input name="TileMatrix" type="zoom" value="18" min="0" max="18"></map-input>
<map-input name="TileCol" type="location" units="tilematrix" axis="column" min="0" max="262144"></map-input>
<map-input name="TileRow" type="location" units="tilematrix" axis="row" min="0" max="262144"></map-input>
<map-link rel="tile" tref="https://server.arcgisonline.com/arcgis/rest/services/NatGeo_World_Map/MapServer/WMTS/tile/1.0.0/NatGeo_World_Map/default/default028mm/{TileMatrix}/{TileRow}/{TileCol}.jpg"></map-link>
</map-extent>
<map-extent label="Imagery" units="OSMTILE" checked>
<map-input name="TileMatrix" type="zoom" value="18" min="0" max="18"></map-input>
<map-input name="TileCol" type="location" units="tilematrix" axis="column" min="0" max="262144"></map-input>
<map-input name="TileRow" type="location" units="tilematrix" axis="row" min="0" max="262144"></map-input>
<map-link rel="tile" tref="https://server.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer/WMTS/tile/1.0.0/World_Imagery/default/default028mm/{TileMatrix}/{TileRow}/{TileCol}.jpg"></map-link>
<map-link rel="tile" tref="https://services.arcgisonline.com/arcgis/rest/services/Reference/World_Boundaries_and_Places/MapServer/WMTS/tile/1.0.0/Reference_World_Boundaries_and_Places/default/default028mm/{TileMatrix}/{TileRow}/{TileCol}.png"></map-link>
</map-extent>
</map-layer>
</mapml-viewer>
WMS Request
The following example shows a Web Map Service Request using <map-link> to request map images.
<mapml-viewer projection="OSMTILE" zoom="4" lat="53.331" lon="-91.667" controls>
<map-layer label="Toporama" checked="">
<map-extent xmlns="http://www.w3.org/1999/xhtml" units="OSMTILE" checked>
<map-input name="z" type="zoom" value="18" min="4" max="18"></map-input>
<map-input name="w" type="width"></map-input>
<map-input name="h" type="height"></map-input>
<map-input name="xmin" type="location" units="pcrs" position="top-left" axis="easting" min="-2.003750834E7" max="2.003750834E7"></map-input>
<map-input name="ymin" type="location" units="pcrs" position="bottom-left" axis="northing" min="-2.003750834E7" max="2.003750834E7"></map-input>
<map-input name="xmax" type="location" units="pcrs" position="top-right" axis="easting" min="-2.003750834E7" max="2.003750834E7"></map-input>
<map-input name="ymax" type="location" units="pcrs" position="top-left" axis="northing" min="-2.003750834E7" max="2.003750834E7"></map-input>
<map-link rel="image" tref="https://wms.ess-ws.nrcan.gc.ca/wms/toporama_en?SERVICE=WMS&REQUEST=GetMap&FORMAT=image/jpeg&TRANSPARENT=FALSE&STYLES=&VERSION=1.3.0&LAYERS=WMS-Toporama&WIDTH={w}&HEIGHT={h}&CRS=EPSG:3857&BBOX={xmin},{ymin},{xmax},{ymax}&m4h=t"></map-link>
</map-extent>
</map-layer>
</mapml-viewer>
