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How to assign Coordinate systems in ArcGIS 10

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I have created a TIN file and various other layers on top. I now need to add a coordinate system to it. The current system is unknown for all layers but the data did come with some x and y grid lines. The map is of an area in South Africa called greyton.

Any suggestions would be very much appreciated!



Melita Kennedy

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Are the digital versions of the data using the same coordinate values as the xy grid lines? South Africa often uses the Lo system. Each zone uses transverse Mercator, but it's south-orientated. That is, the axes are positive south and west.

ArcGIS 10 has some quasi-Lo systems that will work correctly in ArcGIS's easting-northing framework. They're here:

C:\Program Files\ArcGIS\Desktop10.0\Coordinate Systems\Projected Coordinate Systems\National Grids\South Africa

If that's where your ArcGIS is installed. The zone 'number' is the central meridian value. Depending on the age of your data they could be based on the Cape or Hartebeesthoek94 datums.

If the digital data isn't using the same coordinate values, then you'll need to geoference or spatial adjust the data to known data (or the grid lines if you can identify what coordinate system they're using).


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