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Projection Issues

April 28 2008 | 0 comments
Categories: Map Data

I am having issues with projecting data so that all areas overlay eachother where they need to be. First off i want everything to be in NAD83NAD_1983_StatePlane_California_III_FIPS_0403_Feet. The layers I am using are as follows: Soil layer dowloaded from NRCS, city type layer from Esri Data CD, and the problem layer. the top layer is from a preexisting CAD drawing that i want to overlay on top of these layers. In the CAD drawing the layer overlays where it needs to be, but when i bring it into ARC as a converted shapefile, it somehow does not fall onto the correct area. when i check the coordinates of both the ARC and CAD drawings the locations have the same exact coordinate values, but they do not visually lie where the should be. Does anyone have any ideas how to project all these layers so that they fall onto each other. I do know how to project them, but its not working. I am lost here.

Mapping Center Answer:

One thing I do just to make sure I'm not crossing wires, so to speak, is to create a personal geodatabase, then add a feature dataset that uses the coordinate system I need to use. In your case that will be: NAD83NAD_1983_StatePlane_California_III_FIPS_0403_Feet.

Then, I start using the Project tool to add each dataset, starting with the data that I'm most certain of. By certain, I mean the data that I know the projection of for certain. If I'm not certain of any data in particular, I pick the data least want to edit. I make sure of it's datum in order to be sure the transformation method is properly set.

Then I add my second dataset using the project tool. At this point, add both feature classes to ArcMap and verify their coincidence is what I am expecting to see. If so, I add the 3rd dataset and then verify it against the first two datasets. I repeat that for each remaining dataset.

One issue you may have is that the accuracy of either the NRCS or ESRI data may be better or worse than your CAD data. Getting one or the other dataset to conform is a problem of conflation rather than projection or transformation. Try using the spatial adjustment tools as a starter.

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