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I have a worldmap and need to present different countries (e.g. Japan and France) in different extracts in QGIS. Thus I need to find out the best way to decide for an appropriate CRS for the presentation of each country without too much effort. I am intending to then just use the "Project properties" to change the CRS, depending on the country that is currently presented.
How do you decide, which CRS is the most suitable?
For smale areas, the projection of the appropriate UTM zone is always the best choice. You find world coverage UTM zone maps at wikipedia.
For nation wide areas (except USA, Russia and China), the UTM zone for the capital would be best.
For continent-wide presentation, you have to find other solutions. ETRS-LAEA or -LCC would fit for most parts of Europe; US National Atlas Equal Area for North America.
For the whole World, Google Mercator EPSG:3857 is the best choice, though it does not have real metres as units.
I would not prefer WGS84 as presentation CRS, as it looks rather distorted the more to the poles you come.
When choosing a CRS you should be mindful of two things, 1. the scale and extent of your data, and 2. the types of analysis you are running against your data.
For 1, if your data is local to a large scale geography (such as a city or county) you should use a local projection/coordinate system (e.g. NAD 83 Ohio state plane N). If your data is not local at a small scale geography (such as a entire country or multiple countries) you should use a projection/coordinate system that covers a larger area (such as UTM or WGS).
For 2, if your application is running any spatial calculation of measurement of distance on your data your data should be in a projected coordinate system and not a geographic coordinate system.
