Define Projection Failure

[JessicaReilly]

Hello,

I am attempting to define a map projection and to define the correct coordinate system information for Colorado counties layer using ArcToolbox. When I try to 'Define Projection,' Colorado counties is still drawn in California and is not aligned with the US states layer. Any ideas?

Thank you

[SepheFox]

Well, it sounds like you defined it to the incorrect projection. What is the original projection of the data? If you want to change it, you have to use the Project tool instead, by the way.

[DanPatterson_Retired]

The best way is as Seph says...find out what it was supposed to be.  Now if that isn't possible, open a new data frame, move the layer into it, and move your mouse onto the screen and look at its coordinates. Right-click on the layer, select Properties and find its Extents, record the left, right, top and bottom.  If they are in the range of -180 to 180 EW and -90 to 90 NS, then the data were in a geographic coordinate system (GCS aka unprojected) and should have been defined appropriately (in North America, it is some variant of GCS NAD83 or WGS84 (ie gps data)).

If the data had large values in the hundreds of thousands EW and millions NS, then the data should have been  defined in a projected coordinate system (PCS) and you need to know the correct one.  You can't guess...there are thousands but perhaps a half dozen that may be appropriate to your area.

Don't always assume that the file that you 'think' is wrong, since it may have been the first file added to the dataframe...that is why you need to perform those tests in a clean data frame​.

good luck