Specifying a coordinate system
In order for ArcPad to display the layers of your data correctly, they need to be in the same coordinate system or projection. Projection information is stored in a separate file named after the data source but with a .prj file extension—for example, citytrees.prj. ArcPad AXF files and some image formats store the projection information in the file. In addition, each map has an associated projection that can be stored in the ArcPad map (.apm).
The default projection for a new map in ArcPad is latitude– longitude WGS84. If you have an arcpad.prj file in your My ArcPad folder, then it replaces latitude–longitude WGS84 as the default map projection.
When you add a layer or map with a different projection to a new map, the data’s projection replaces the default projection.
If you add a layer with no projection (.prj file) to a map with a geographic projection, ArcPad checks if the data appears to be latitude– longitude (i.e., geographic). If it appears to be geographic, ArcPad asks if you would like to assume the data is in the same geographic projection as the map. If it does not appear to be geographic, ArcPad removes the default projection and the map has no projection.
Convert GPS input data: ArcPad supports on-the-fly projection and datum conversion from the (geographic) GPS input map datum to the projection of the current map
Convert your data: Use ArcGIS Desktop to change the projection of your data before adding it to your ArcPad map.
For information about supported projections and datums, refer to the ArcPad Reference Guide.