Auxiliary themes are optional input to FlamMap. They do not contribute to generating FlamMap output, but they are handy for orienting and viewing results.
There are four types of Auxiliary Themes that can be loaded into FlamMap,
Auxiliary Grid Themes can be in ASCII Grid or GeoTIFF formats. The other three theme types must be in shapefile format. Click on the above links for more information about the individual Auxiliary Theme types.