Georeferencing rasters

Sometimes, you have a paper map, an image of a map from the Internet, or even a raster file with projection data included. When working with these types of data, the first thing you'll need to do is reference them to existing spatial data so that they will work with your other data and GIS tools. This recipe will walk you through the process to reference your raster (image) data, called georeferencing.

Getting ready

You'll need a raster that lacks spatial reference information; that is, unknown projection according to QGIS. You'll also need a second layer (reference map) that is known and you can use for reference points. The exception to this is, if you have a paper map that has coordinates marked on it or a spatial dataset that just didn't come with a reference file but you happen to know its CRS/SRS definition. Load your reference map in QGIS.

This book's data includes a scanned USGS topographic map that's missing its o38121e7.tif projection information. This map is...