Projections

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The Earth is spherical, but all computer screens and paper maps are flat. A map projection ‘projects’ (converts) the Earth’s spherical surface to a flat two dimensional representation. This always requires some distortion, and many projections have been developed to reduce certain aspects of this distortion. As well as global map projections, many have been developed for individual regions, countries, and even provinces. For example, the UK uses a “Transverse Mercator” projection that is aligned perfectly over the UK. Similarly, Russia uses a conical projection that is designed to cover a wide range of longitudes.

Maptitude supports a range of map projections that are in widespread use. By default it will choose the best map projection for your current view window, but you can override this choice if you wish. You do this from the Map Properties dialog box (select File->Properties on the main menu):

The Map Properties dialog box

The Map Properties dialog box

Here, the map has been zoomed out to show the entire world, and Maptitude has selected the Eckert IV projection. This is what it looks like:

World map drawn with the Eckert IV map projection. This is Maptitude's default for world maps.

World map drawn with the Eckert IV map projection. This is Maptitude’s default for world maps.

Equal area maps such as the Eckert IV are perfect for statistical applications where relative size is important.

To override the choice, clear the Auto Projections checkbox, and press the Change Projection dialog box to display the Projection and Coordinate System dialog box:

The Projection and Coordinate System dialog box.

The Projection and Coordinate System dialog box.

Maptitude has the different projections sorted into classes according to their application, e.g. US, North polar region, equatorial regions. Here we have a world map, and we have selected the Bonne projection. This is another equal area projection but it has a distinctive heart shape reminiscent of the famous Waldseemüller map, and looks like this:

The distinctive Bonne map projection

The distinctive Bonne map projection

Note that both of these projections are non-conformal: shape and direction are distorted. Neither are suitable for navigation. Gerard Mercator developed his famous Mercator projection specifically to aid navigation at high latitudes:

Notice that even the shape of Greenland is pretty good, and more importantly directions are preserved. A compass can be laid on this map, and the measured bearing will be correct. However, size is badly distorted. Both Greenland and Antarctica are shown many times their real size. Therefore even though this is probably the most common map projection in widespread use, it should never be used for statistical map plots! When set to use Auto Projections, Maptitude will always choose an equal area projection instead.

A third class of projection are the equidistant projections. These are centered on an important location such as a pole or a capital city. Distances from this central point are then preserved. These are less common now, but were quite popular when a country might commission a map to show distances from their capital.

The different map projections and their strengths and deficiencies are further discussed on a series of blog posts that I have written.

Further information can also be found in John P. Snyder’s Flattening the Earth: Two Thousand Years of Map Projections.

2 comments to Projections

  • Abi Dhakal

    In Maptitude how do I check to know the projection of a shapefile. Usually, when I am sent a shape file created in Maptitude it does not have a projection file with it.

    Thank you very much.

    Abi

    • On the “Export Geography” dialog box, there are various options. Select “Esri Shape” for a shapefile.

      Press the “Coordinates” button in the lower right to set the coordinate system. This includes projection transformations.

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