How many layers of data (Shapefiles and imagery) can be displayed at once?
There is no limit to how many layers you may have turned on at one time. Keep in mind, however, that the more layers you have in your view, the longer the map takes to be displayed. In addition, you may not be able to interpret the map because of overlapping symbology. For example, it might be difficult to interpret a map that has topography, bedrock geology, soils, DEP owned property, roads and trails, and water quality classifications all displayed at once.
