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I have a client, that needs some geological maps digitized (polygons) in a Cartesian grid. It would be a basic, square grid with North up, and coordinates in x and y. Some of the maps will need to be digitized in meters and some in feet. I've looked around a lot for a way to set this up in QGIS, but I can't find anything that I can understand.

I think if my technical knowledge was better, I could make a custom projection that would work. I'm baffled that this answer isn't easier to find. Although I wouldn't be surprised if I'm overlooking something.

I'm not interested in placing this spatially. It can stay in the Cartesian grid. I'm doing the digitizing in QGIS and he is placing the SHP files into MapInfo for plotting.

Edit: A question that I've been wondering is if it is fine to digitize in a UTM grid as a SHP file, then just delete the PRJ? Would the SHP file then have the right coordinates in a flat plane? Or is there more to it than that?

Thanks,

cndnflyr
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1 Answers1

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A custom transverse mercator projection is a good idea. You just need a reference point in WGS84 coordinates as a center of the projection.

You can see an example here:

Using customized Coordinate System in ArcGIS Desktop?

All you need to change is lat_0 and lon_0 (and don't mix them up). These are the WGS84 coordinates of your local origin. You can take them from a GPS unit if you have no official values.

Since your y-axis is North, you don't need the mentioned omerc projection.

If you delete the .prj file, you will have no reference to import the data into Mapinfo or any other GIS programme.

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AndreJ
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  • This is part of my problem, not knowing how to apply a custom projection in a way that will give me the results I'm looking for. In QGIS there is no guidance. I can give the custom CRS a name, and then there is a scary, empty white box called 'Parameters' that I don't know what to do with. The examples that I have found don't do much to explain what I need to edit and how, to get a basic, square x, y grid. – cndnflyr May 13 '14 at 04:28
  • I explained that a bit further on another post. See my extended answer. – AndreJ May 13 '14 at 05:42