I'm trying to use the kernel density tool for some point data. The area units is greyed out as square map units. I know that in order to fix this I need to project the data so that it is in some sort of meters, or feet etc. The problem is that the point data is spread throughout the US. I'm not sure what would be the best projected coordinate system for this point data that would enable the area units option so I can do square miles or square kilometers. Would anybody be able to give a suggestion for this? Any help would be greatly appreciated.