Geographic Projections

When displaying maps of the world on a flat surface, a projection is necessary to go from a spherical coordinate system (the Earth) to a rectangular or Cartesian system (the paper map or the computer screen). Several projections are available in JMap Admin. Some projections are adequate for relatively small regions while some are appropriate for displaying very large areas (e.g. continents). For more information, see the definition on Wikipedia.

When you create a spatial data source in JMap Admin, you must inform JMap of the projection in use by the data (if any). If you do so, you will later be able to change the projection used to display your data in JMap (in the project configuration). This is very useful when you need to integrate data sets that use different projections and coordinate systems. If your data is using longitude and latitude values (degrees), it is not projected. In this case, select Longitude/Latitude as the projection choice. If your data is not using a world coordinate system (sometimes called non-Earth), which is typical with CAD files, then select Unknown. You will not be able to change the display projection later on.

Supported projections in JMap are listed in file JMAP_HOME/conf/projections.properties. New projection classes can be developed using JMap SDK. If new projection parameters need to be added, this should be done in a file called customprojections.properties to avoid loosing your changes at the next JMap upgrade.