I'm creating A4 maps to show where forest cover and mining fields overlap across the globe. Each A4 map focuses on a specific country (e.g. India, USA, China, Australia...). For each country, I need to calculate how much overlap / intersection there is between the forest cover in that country and the mining fields to work out the area of forest that is threatened by mining activity.

I have sourced / received the following data:

World country boundaries (polygons, Geographic coordinate system WGS_1984, Datum D_WGS_1984)

Global forest cover (polygons, Geographic coordinate system WGS_1984, Datum D_WGS_1984)

Mining areas (polygons in multiple Geographic coordinate systems e.g.) Australia - GCS GDA94 India - GCS WGS_1984 Indonesia - GCS WGS_1984

To calculate areas (including total mining area, total forest area and overlap between the two) I need to work in a projected coordinate system (as area calculations are disabled in global coordinate systems).

Can someone please advise which projection I should chose?

Normally I would opt to work in a UTM zone but when dealing with large countries like Australia this warps the shape of the country on the map.

The area calculations (in sqkm) are also altered quite dramatically depending on the projection I use.

Can someone recommend a projected coordinate system that I can suitably use for all the country maps and that will produce the most accurate area calculations?

  • You're going to want an equal area projection like Albers. Not sure what a good one is for the whole world. – Baltok Nov 13 '15 at 14:59

Sounds like you're prepared to use different coordinate systems for different countries. Where possible, UTM, as you mention, would be an excellent choice.

For countries that are too large for that, I suggest Sinusoidal, or Cylindrical Equal Area, or Albers Equal Area Conic. In all cases you can manipulate the central meridian and standard parallel(s) so that your country of interest lies in the centre of the map, so that it doesn't look too distorted to a viewer (especially in the Sinusoidal case).

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You can use Web Mercator (like google) which shares some of the same properties of the standard Mercator projection: north is up everywhere, meridians are equally spaced vertical lines, but areas near the poles are greatly exaggerated.

Unlike the ellipsoidal Mercator and spherical Mercator, the Web Mercator is not quite conformal due to its use of ellipsoidal datum geographical coordinates against a spherical projection. Rhumb lines are not straight lines. The benefit is that the spherical form is much simpler to calculate, saving many computing cycles.

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