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I have a blank map, I've set the data frame to the same projected coordinate system as the data I'm going to add. I have added one shapefile and it looks good. When I wave the cursor over the map the decimal degrees displayed in the lower right corner of the data frame are correct.

I then attempted to add a Excel table that has lots of points with the decimal degrees for each point. I added the table, and used the Display XY Data option to display the points. The resulting points do not overlap the first shapefile, even though the two are actually just about identical. I've checked the projected and geographic coordinate systems and they're the same.

When I zoom in on the layer with the points I find that in the lower right hand corner of the data frame it registers everything as being at -85.489, 0 decimal degrees, which is clearly wrong. The measure tool shows that the points are mere millimeters apart, which they're not.

Based on similar question on this site I tried using the project tool on my points and projecting it into the format it already was in (i.e. the same projected and geographic systems as the shapefile) that didn't work, it just wound up warped.

What has gone wrong with displaying my data?

vt32
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    First, note the coordinate display in the lower right can be set independently of the dataframe CRS. Next, if using a projected CRS units shouldn't be decimal degrees, it would likely be meters or feet for units. If you have a decimal degree coordinate list and are adding those to a projected dataframe without specifying their CRS as geographic, they won't come in at the right place. The other possibility/extension of that is one of your two datasets has an incorrectly defined projection. Reprojecting only works from known/correct CRS to another CRS. What CRS is your non-Excel data? – Chris W Apr 07 '15 at 18:37
  • I think it would be useful if you said what coordinate systems you're using. If your table coordinates are in decimal degrees, and you Display XY Data with ANY geographic coordinate system, they should at least be close. My guess is that you are choosing a projected crs at that step. – mr.adam Apr 07 '15 at 18:38
  • Sorry, GIS newbie here. My non-excel data is NAD 1983, when I display the xy data of the excel file it then says it's also in NAD 1983. My excel data is points whose coordinates I got from Google Earth. – vt32 Apr 07 '15 at 18:41
  • It sounds to me like what you're saying is that my excel file has points that have coordinates from a Geographic Coordinate System, while the shapefile I'm trying to match them to is a Projected Coordinate System, and for some reason Displaying the XY Data doesn't cause it to project correctly all on its own. – vt32 Apr 07 '15 at 18:52

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I’m still not quite sure what went wrong when I hit the “Display XY Data” button, but here’s the work-around that fixed it;

I made a new map and put the dataframe into WGS 1984. I then added the excel file and selected Display XY Data. Once that came up I exported that into a shapefile.

I then opened a new map, set the dataframe to NAD 1983 (the projected coordinate system of my map layer).

I added the map, and then added the shapefile with my points. They lined up perfectly. I’m assuming the shapefile was re-projected somehow automatically.

Kind of a laborious work-around and probably not the right way to do it, but it worked out okay.

vt32
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  • NAD83 isn't projected, it's geographic. More properly a datum and very similar to WGS84 (also geographic and not projected). "NAD 1983 Contiguous USA Albers" is a projected CRS using the NAD83 datum. And yes, in ArcGIS you're dealing with on-the-fly reprojection. If a dataframe doesn't have a defined CRS, it takes that of the first defined data added to it. If it does have one defined, all subsequently added layers are reprojected to that CRS (with possible warnings about a transformation being required). XY table doesn't have a CRS, so you either tell it one or it assumes dataframe's. – Chris W Apr 07 '15 at 21:08