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Projection Issues

July 02 2008 | 0 comments
Categories: Map Data

I have two data sets concerning historical crop data for Kern County Ca. They both have the same projection: NAD 83 State Plane California Zone 5. One Shapefile "falls" exactly where it needs to be in relation to the coutny lines and aerial photographs. The second set of shapefiles, even though they have the same projection, are shifted to the right about 300 feet. You can see with the two different shapefiles that they are similar in shape. They just don't overlay eachother. I have attached what i am looking at; the blue lines are in the correct position whereas the orange are not.
Any ideas as to how i can fix this shift?

Mapping Center Answer:

It seems likely that the 2nd set of shapefiles have their coordinate system incorrectly defined. Check the history of that dataset and hopefully you'll learn what the correct coordinate system is.  If you do, then use the Define Projection tool to set it properly.

If you don't find anything about the data, then one thing to check is whether it was just a NAD27 / NAD83 problem.  They way to find out is to use the Define projection tool to set the coordinate system to NAD27 State Plane California Zone 5.   Then use the Project tool to project and transform that into NAD83 State Plane California Zone 5. 

Another possibility is that the data is actually another of the state plane zones.  Just use the Project tool to project one of the datasets to the other zones and test it.

We also have a help topic that deals more generally with this problem called Identifying an unknown coordinate system.

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