How to convert coordinates from meters to decimal degrees?

Question

I have a shape file. The coordinates (Lat/Long) are projected as meter (555000, 155000). But, I want to re-project it to decimal degrees(51.523666, -0.07467). How can I do it with ArcMap or Quantum GIS?

Thanks, In advance

Answer 1

In QGIS, it's very straightforward. First, ensure that you have the correct coordinate system for your original shapefile:

1. Add the layer to the map canvas;
2. Right-click on the layer and select "Set layer CRS";
3. Choose the correct coordinate reference system (CRS) from the list - it is probably in UTM (a metric grid) and you will have to know the zone and datum for the data; it may be already automatically selected!

After this:

1. You right-click on the layer and select "Save as ...":
2. Click 'Browse' near CRS in the resulting dialog and select WGS84 EPSG:4326 as the CRS for the new file - this will save it with decimal degrees as the coordinate system.

It's a very good idea to make sure you select a good name in the "Save as" dialog - appending the coordinate system to the name can be very helpful, e.g. my_shape_file_DD_WGS84 to remember that it's in degrees, WGS84.

Answer 2

You will need to know the coordinate system of the projected data and then change it base to decimal degrees using the Project tool in the data management toolset if you want to do it in ArcMap. The define projection tool can be used to establish a coordinate system for the input file if it is unknown.