One problem that is pervasive in the world of GIS is coordinating coordinate reference systems (the overarching category that includes projected coordinate systems and geographic coordinate systems).
When you download files from any source, take care to see if they indicate the CRS/SRS or Projection for the data. This information is crucial both for imagery and for vector files.
In the case of Shape Files, you'll often see the .prj file with the rest of the files (.dbf, .shp, .shx), and that contains the Projection information. In this case, you're set.
With imagery, though, the situation isn't as good. Often times imagery has georeference information (in the form of a .pgw, .jgw, .tfw, or .wld file) but no information on what coordinate system those coordinates reference. In this case, data in a like coordinate system will display fine, but data in other coordinate systems will not mesh. Further, distance calculations could be massively incorrect.
The key to solving these problems is to set the Projection on the layer using Layer > Set Layer's Projection... But, to do this, you're going to need to have the original information from the source of the data. There are a lot of common coordinate systems that are known to Cartographica, so you might be able to guess, but it's always best to go back to the source and look for an explicit statement there.
Have more questions? Submit a request
Comments