Choosing an SRS

So how do you choose a suitable SRS for your own geospatial datasets and GIS projects?

Some questions to consider:

1. What type of coordinates do you use in your fieldwork? Latitude-Longitude, or a projected coordinate system?
2. If projected, do you know the name of the map projection you use?
3. Do you know which datum that map projection uses?
4. Are all of your spatial datasets in the same SRS?

You can find out about relevant SRSs from a variety of sources:

• Ask colleagues or friends who work in the same geographic area as you
• Local topographic or road maps on paper - see the legend, or look at the coordinate numbers in the map margins
• Search online for information about your geographic area, e.g. national mapping agency
• Look on the Spatial Reference website
• Try the EPSG map search
• Try adding your existing geospatial datasets to QGIS - open the layer Properties to see what QGIS thinks their SRS is

Now think about why you use that SRS. For example:

• You’ve been advised to by others more knowledgeable in GIS
• Simplicity of understanding coordinates
• Easier to estimate distances between locations on the ground
• For compatibility with legacy geospatial data such as old survey records
• For compatibility with online data sources
• To allow spatial analysis

Post a response in the community forum:

1. What spatial reference system(s) do you use, and why?
2. Will you change the SRS you’re using based on what you’ve learned in this module?

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