Projection Issues

[MikeWissner]

Hello All,

I have a dataset with Lat/Long values that I need to display.  Before displaying, I imported the coordinate system from the first layer that I added to the map.  However, the XY data, when displayed, does not coincide with the base layer. 

Both the GCS and the PCS match in the Properties --> Source tab.  Projections continually frustrate me.  Can anyone explain to me why these two datasets have the same GCS and PCS in the source tab, but do not line up?

Also, I tried the project tool as well as the Define Projection tool and neither worked.  I receive the following error:

000289 : Failed to alter spatial reference.

Then I started over and got a successful Project result, yet the data did not move.

Please help.

Any assistance is much appreciated,
mike

[LucasDanzinger]

Hi Mike,

It's hard to say what is going on without looking at your data, but perhaps the wrong coordinate system is defined. This would mean it is set as a certain coordinate system in the properties, but it really isn't that coordinate system. For example, you could have data gathered in WGS 1984 and then go in and Define the Projection as NAD 1983 UTM Zone 15N. That doesn't mean that the data are actually NAD 1983 UTM Zone 15N, rather it means that you simply gave your data that label. You only want to use the Define Projection tool when either your data do not have a coordinate system defined (gathered the data in WGS 1984 and it says Undefined in the Source Tab) OR if someone defined it incorrectly (defined it as NAD 1983 UTM Zone 15N when it is WGS 1984). The Project tool will actually physically reproject the data from one coordinate system to another (and not just change the label as Define Projection does). For example, you could use it to project your data from WGS 1984 to NAD 1983 UTM Zone 15N. As far as why your data aren't lining up, it might be that the incorrect coordinate system is defined. This would be my best guess, being that you said the GCS and PCS are listed as the same. You could either try to gather the correct information from the data source, or read through the "Identify the spatial reference, projection, or coordinate system of data" KB article. An important thing to check (which is highlighted in the article) is how many digits are to the left of the decimal place for the extent in the Source tab.

[HardolphWasteneys · Accepted solution]

Mike,

reading between the lines of your question I think Lucas's suggestion  "For example, you could have data gathered in WGS 1984 and then go in and Define the Projection as NAD 1983 UTM Zone 15N. That doesn't mean that the data are actually NAD 1983 UTM Zone 15N, rather it means that you simply gave your data that label." is on the mark.

I would infer that you have defined the lat/long data as projected when in fact they are not so they are being displayed as through degrees of lat and long were just meters.

Go back and re-add the XY Data, but when it comes to entering the coordinate system (the EDIT ... button) only enter a Geographic Coordinate System, WGS 84, NAD 83 etc.  Ditch the previously created shapefile. 

The base layer's coordinate system is irrelevant as is that of the Data Frame.  The GIsystem just has to know what kind of units the numbers in the spreadsheet represent and in what coordinate reference frame they were measured in order to digest them properly.

Hardolph

[MikeWissner]

Thank you both,

you were both spot on.  I Started from scratch and instead of importing the coordinate system, I just selected the appropriate GCS and it worked.

I apologize for the elementary question, but a thorough understanding of how to handle projections has still eluded me.


best, mike