Most larger scale print maps are 2D plan. Every point on this kind of map is viewed from directly overhead. The viewpoint is at infinity so the viewer looks vertically down the Z axis along parallel projection lines.
This means there is no obvious indication of elevation as only the X and Y coordinates can be plotted. Cartographers get around this problem by using various tricks. Commonly-used techniques include the addition of contour lines, spot heights, hillshading and hypsometric colour.
Many people find maps easier to relate to if they are displayed in three dimensions rather than two.
Most existing 3D maps have a fixed viewpoint, which means we have a perspective view with converging projection lines. We call this an oblique or 3D perspective (the terms 3D and oblique are interchangeable in this context). The 3D perspective view looks familiar to us because it is what we see with the naked eye. However it doesn’t always make for good maps.
- there is usually large variation in direction and distance.
- the focus is on the centre of the view and peripheral areas appear distorted.
- significant areas in the view may be occluded (hidden from view).
These drawbacks are all due to the convergent projection lines. So in recent years, we have seen the development of improved digital techniques for generating 3D maps with parallel projection lines.
One example is the Plan Oblique (so-called because it sits on a planimetric base). This 3D projection addresses most of the issues found with 3D perspective maps.
We generally prefer a compressed derivative of the plan oblique, a projection we call the Parallel Oblique. Although it has more disadvantages compared to the Plan Oblique (less useful for measuring distances for example), we consider it works better at larger map scales and looks more realistic.
A Profile map is a special case of a 2D plan map where the viewer looks not down the vertical z axis but horizontally along either the X or the Y axis. Profile maps are used to produce ground-level silhouettes of the landscape.