We sent a spreadsheet with decimal Lat/Long data. The receiver used this and sent back a spreadsheet with their data. Their Lat/Long values were much different. I supected a projections issues and began to dig in and learn more. I converted both to points in ArcMap and there were big differences (hundreds of feet in some cases). I started by trying to project my lat/long points to another geographic system to come close to theirs. (I'm haven't gotten an email response from them yet).

Using the "Calculate Geometry..." option from the right click menu in the attribute table, I can calculat the X or Y using the data frame or the data set coordinate system. Nice!

When I change the data frame projection, and recalculate the X Y I don't always get different results. For example, WGS72 and WGS84 give me exactly the same Lat/Long. Some projections drop the decimal places in the decimal degrees, some drop the decimals in the results in feet.

Any info sources or websites out there to understand the limits on these projections and why the decimal places are sometimes dropped?

Thanks in advance.

**Edited by Mark Boucher, 26 August 2010 - 07:45 PM.**