mapml-meta-markup

name	mapml-meta-markup
description	Tells you how to correctly create and edit the markup for a <map-meta> element. Use it when generating MapML output markup in an HTML page or XHTML MapML document.

The <map-meta> element is an extended HTML meta element, for use in Web maps.

Attributes

name

The name attribute identifies the type of metadata that is being set. Possible values of name related to maps include:

Name	Description
projection	Set the projection for the document
extent	Define the bounds of the document in terms of corner position keywords and axis names, potentially combined with a zoom value if necessary (depending on coordinate system).
cs	Identifies the default coordinate reference system of coordinate strings found in the document.
zoom	Specify the zoom range min, max and default zoom value for displaying the document contents. The 'native' zoom range of templated map content is specified by the min/max attributes of associated zoom inputs. If templated content is not described by associated zoom input min/max/value attributes, the values specified in a <map-meta name=zoom> will be used as fallback, if it exists. If no <map-meta name=zoom> exists, the corresponding min/max values from the projection will be used.

---

content

name	content value
projection	A case-sensitive projection name, or a custom projection name
extent	((position keyword)-(axis name)=(axis value)(,))4(,)(zoom=(zoom value))0,1
cs	A case-sensitive coordinate system abbreviation.
zoom	(min=minimum zoom value,max=maximum zoom value,)(value=current zoom value)

:::tip

The grammar rules for the <map-meta name="extent" content="..."></map-meta> content attribute require that you specify coordinates of the top-left and bottom-right corners of the extent being marked up. You must specify the axis values of the extent as values for a set of four comma-separated keys which identify the coordinate system being used (i.e. pcrs, gcrs, tile, tilematrix, map or tcrs) by virtue of the axis names. For example top-left-easting=-8433179 identifies that the coordinate system being used is pcrs. You cannot mix coordinate systems within a single content attribute value, for example top-left-easting=-8433179, top-left-latitude=49.02174,... is not legal.

You can copy a correctly marked-up <map-meta name="extent" content="..."> value onto the clipboard for the current map viewport, in pcrs coordinates (by default), via the map context menu Copy > Extent item as shown below:

:::

---

Content categories	Metadata content
Permitted content	None, it is an empty element.
Tag omission	While the HTML <meta> element is a void element, the polyfill <map-link> must have an end tag.
Permitted parents	Inline: the <map-layer> element. In a MapML document: the <map-head> element.
Implicit ARIA role	No corresponding role
Permitted ARIA roles	No role permitted
DOM interface	HTMLMetaElement extension

---

Examples

Setting zoom

Using the <map-meta> element to specify the native zoom and fallback zoom range for a <map-feature>. The coordinate encoding is narrowly determined for the feature, by the <map-geometry cs="gcrs"> attribute, which tells the polyfill how to parse and process strings of coordinates found in descendant <map-coordinates> elements.

<map-layer label="Favourite Restaurant" checked>
  <map-meta name="projection" content="OSMTILE"></map-meta>
  <map-meta name="zoom" content="min=0,max=22,value=3"></map-meta>
  <map-feature>
    <map-featurecaption>Big Daddy's Crab Shack</map-featurecaption>
      <map-geometry cs="gcrs">
          <map-point>
            <map-coordinates>-75.690276 45.41868</map-coordinates>
          </map-point>
      </map-geometry>
  </map-feature>
</map-layer>

Setting extent

Using the <map-meta> element to establish the pcrs (easting,northing) extent of a map layer, the coordinates of which are encoded as gcrs pairs.

<map-layer label="Favourite Restaurant" checked>
  <map-meta name="projection" content="OSMTILE"></map-meta>
  <map-meta name="zoom" content="min=0,max=22,value=3"></map-meta>
  <map-meta name="extent" content="top-left-easting=-8433179, top-left-northing=5689316, bottom-right-easting=-8420968,bottom-right-northing=5683139"></map-meta>
  <map-feature>
    <map-featurecaption>Big Daddy's Crab Shack</map-featurecaption>
      <map-geometry cs="gcrs">
          <map-point>
            <map-coordinates>-75.690276 45.41868</map-coordinates>
          </map-point>
      </map-geometry>
  </map-feature>
</map-layer>

Fallback cs for <map-geometry>

Using the <map-meta> to specify a fallback coordinate encoding for geometries in the layer. The encoding of the coordinates is identified by the use of the <map-meta name="cs" content="gcrs"> element. Such a declaration tells the polyfill how to parse and process any coordinates that don't have an ancestor <map-geometry cs=""> coordinate encoding declaration. Note that the zoom level at which the feature should be displayed is not specified, nor the extent. Both values will fall back to the default values for the projection.

<map-layer label="Favourite Restaurant" checked>
  <map-meta name="projection" content="OSMTILE"></map-meta>
  <map-meta name="cs" content="gcrs" ></map-meta>
  <map-feature>
    <map-featurecaption>Big Daddy's Crab Shack</map-featurecaption>
      <map-geometry>
          <map-point>
            <map-coordinates>-75.690276 45.41868</map-coordinates>
          </map-point>
      </map-geometry>
  </map-feature>
</map-layer>

Default metadata

Allowing all metadata values to default to those of the map's projection. The feature will be displayed at all zoom levels, and the coordinates are by default interpreted to be gcrs (longitude latitude). The extent of the layer defaults to that of the projection.

<map-layer label="Favourite Restaurant" checked>
  <map-feature>
    <map-featurecaption>Big Daddy's Crab Shack</map-featurecaption>
      <map-geometry>
          <map-point>
            <map-coordinates>-75.690276 45.41868</map-coordinates>
          </map-point>
      </map-geometry>
  </map-feature>
</map-layer>