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I am trying to understand this command:

ogr2ogr -f "MapInfo File" wgs84.shp -s_srs EPSG:27700 -t_srs EPSG:4326

I don't understand the s_srs and t_srs paramaters. The help file says that the commands "override the source srs."

I am new to GIS. What is SRS? Is this a map making term? It is hard to google.

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Spatial reference system? – Martin Feb 11 '14 at 15:37
SRS is the same as CRS. – AndreJ Feb 11 '14 at 15:42
up vote 8 down vote accepted

SRS is the spatial reference system that your data are stored in. The terms SRS and CRS are often used interchangeably. The SRS defines the projection and map units (commonly degrees or meters) of the data.

In OGR2OGR the -s_srs switch allows you to manually specify an SRS, which may be different to the SRS recorded with the input data. You might use this if you know that the SRS of the data is wrong or perhaps the data are projected but has lost its SRS information (e.g. a shapefile without a .prj file). If you omit this switch ogr2ogr will try to read the input data's srs. The -t_srs switch allows you to transform the data to a new SRS (i.e. your output is in a different projection/coordinate system to the input).

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