I have downloaded some shapefiles from two different sources both of which show different aspects of the same area.

However, they have different Coordinate reference systems. One has the reference system GCS_Airy 1830, while the other has OSBG_1936_British_National_Grid.

Will this prove to be an issue down the line, and if so how do I choose between the two systems?


As I understand it GCS_Airy_1830 is the datum for the projected coordinate system OSBG_1936_British_National_Grid. So they are not different coordinate systems. A datum is a component of a coordinate system. As you are working on data in the UK ensure your datasets are projected into the British National Grid, this will make subsequently mapping and analysis stress free.

  • Thank you for the clarification, I will do so from now on!
    – tom91
    Mar 28 '19 at 8:04
  • To get the data into BNG, redefine (in ArcGIS, Define Projection tool) to OSGB 1936 first, then use Project tool to change to BNG. Otherwise, you may get a warning or requirement asking about a geographic/datum transformation.
    – mkennedy
    Mar 28 '19 at 9:47

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