Hi All - I have an issue that has been nagging me forever. Here's an example. I have a layer in a map, and under Properties > Source it shows "Projected Coordinate System: NAD_1983_UTM_Zone_11N" and "Geographic Coordinate System: GCS_North_American_1983". My first question is: am I working with a projected, or a geographic coordinate system? Second: what is NAD 83? Third: is UTM a projected or geographic coordinate system? I'm so freaking confused! The more I look into it the less clear it becomes!
Lastly, when I open the attribute table, create a new field, field type double, etc... calculate geometry the only option I have is to calculate "X coordinate of point" or "Y coordinate of point". Why can't I calculate lat/long in minutes, seconds, etc? What if I wan't both in the same attribute table?
I'm thinking the answers to the first set of questions are huge, and that I know so little about it that I don't even really know how to ask the question. Any help would be greatly appreciated!
Yes, you have a lot of questions that have long answers! First, have you tried reading the map projections guide book in the help? There are several topics each on geographic and projected coordinate systems.
Geographic coordinate system: provides a frame work / reference system for locating positions on a spheroid or ellipsoid. Positions are located using angles and angular units. "Earth model". When displayed in 2D, it's actually projected using something like the Plate Carree map projection.
Projected coordinate system: Two-dimensional framework / reference system for location positions. Includes a GCS as part of its definition. Has to distort data to crush the 3D surface into 2D: distance, shape, area using a map projection and parameters customized for a particular area.
NAD 83 / NAD 1983 / North American Datum 1983: a GCS built using data from Canada, US, ?and Mexico? Finished in 1986 before GPS really got going, there have re-adjustments since in both Canada and the US. Canada: CSRS. US: HPGN / HARN, NSRS2007, and 2011.
UTM: Universal Transverse Mercator. A grid system designed by the military. It's divided into 6 degree wide zones (there are a few exceptions) and covers the entire world. The map projection is transverse Mercator, with similar parameter values for each zone. The poles have separate UPS zones that use the stereographic projection. Can be used with any GCS, although the military uses WGS84 almost exclusively.
DMS is a string format, not a double value. You can store only one value per double precision field, but can certainly add two fields to a table! You may need to set the data frame to a geographic coordinate system first. Also check out the Convert Coordinate Notation tool.
Nonetheless, I strongly recommend you to take serious time to familiarize yourself with the basic concepts, as the consequences of inappropriate and incorrect usage can be devastating (yes, not only on paper but also literally, I once worked a short period for an oil company, and they had a special introduction to coordinate systems for new employees working in GIS that started with an oil platform going up in flames due to wrong usage of coordinate system information - this was no joke!)
Read as much as you can from different sources, ultimately, things should start to clear up a bit.