Editing Template:Location map/Creating a new map definition (section)

== Map definition data ==
{{expand section|date=August 2011}}

The templates utilize any one of a set of map definitions. These are not forks but rather auxiliary pages and must have names following the pattern "Module:Location map/data/''location''" or "Template:Location map ''location''", where ''location'' is the name of the area covered by the map. The template space is supported only for backward compatibility; all new map definitions should be created as modules. '''Important:''' If a new map has the same projection and boundaries as the old map (such as [[:File:Iraq location map.svg]] and [[:File:Iraq location map2.svg]]), a new definition should '''not''' be created; instead, the old definition should be used with the AlternativeMap parameter. To create a simple map definition module using an image of a map with an [[equirectangular projection]] having the equator as its standard parallel (aka plate carrée, “unprojected”, lat/lon projection):

# Create a new map image and upload it to [[commons:Main Page|Wikimedia commons]] or find an existing map on the same site.
# Create a module named Module:Location map/data/''location'', copy the content below into it and substitute the appropriate values.
# Create a page named Module:Location map/data/''location''/doc and follow the instructions under [[#Documentation]].

As an example of a map that uses an equirectangular projection, we use [[Module:Location map/data/Belgium]]. Please do not experiment using active templates.

<syntaxhighlight lang="lua">return {
	name = 'Belgium',
	top = 51.8,
	bottom = 49.2,
	left = 2.2,
	right = 6.9,
	image = 'Belgium location map.svg',
	image1 = 'Belgium relief location map.jpg'
}</syntaxhighlight>

{| class="wikitable" style="width: 50%;"
! Parameter
! Description
|-
| <code>name</code>
| The name of the area covered
|-
| <code>top</code>
| The latitude of the top edge of the image using [[decimal degrees]]
|-
| <code>bottom</code>
| The latitude of the bottom edge of the image
|-
| <code>left</code>
| longitude of the left edges of the image
|-
| <code>right</code>
| longitude of the right edges of the image
|-
| <code>image</code>
| The name of the image file on Commons
|-
| <code>image1</code>
| The name of an alternate image, usually a relief map, which can be accessed using the <code>relief</code> parameter.
|}

Maps of this type will work for small to mid sized areas. [[Module:Location map/data/USA Alabama]] is another example of a map description that uses an equirectangular projection. Notice that the image of the country is not what most would expect. 

=== Advanced projections ===

Maps that use other projections, such as [[Module:Location map/data/USA]], which uses an equidistant [[conic projection]]. require formulas which are used to calculate the <code>x</code> and <code>y</code> coordinates for the location mark. Understanding these formulas requires a familiarity with the subject, so you are more than welcome to skip this section.

The input $1 is the latitude and $2 is the longitude, both in decimal form. The expression follows the syntax of [[mw:Help:Extension:ParserFunctions##expr|ParserFunction "#expr"]]. The two output coordinates are defined such that the formula for <code>x</code> evaluates to 0 for the left edge of the image and 100 for the right edge; the formula for <code>y</code> evaluates to 0 for the top edge and 100 for the bottom edge.