Meteorologists use maps in virtually every facet of their work. They use them to analyse the pressure distribution and compute the wind, to visualise where it is warm or cold, and to depict the areas where rain or snow may fall. They use maps to illustrate the future weather, and to reconstruct the climate of the distant past. Meteorology, in a sense, is made of maps. But therein lies a problem. Only a globe can represent the spheroid Earth with anything approaching perfect accuracy; any attempt to represent it on a sheet of paper or computer screen imports distortion. Maps, therefore, are often classified by the property which is best preserved, without distortion, when the relevant area is "projected" by various methods onto a flat piece of paper.
An equal-area projection, for example, is one where all areas depicted on the map have the same proportional relationship to their equivalent ground areas in real life. On a global scale, this can be achieved by a cylindrical projection. The globe is imagined to have a cylinder of paper around it touching it at the equator, and the planes defined by the circles of latitude are imagined extended to intersect this cylinder. If the paper is then unrolled with the projected pattern kept intact, the resulting map of the world has horizontal lines for the lines of latitude, and straight, parallel, vertical lines for the meridians; the map is "equal area", but shape, distances and bearings are all distorted.
A map is conformal, on the other hand, if its scale is everywhere preserved, which has the additional benefit that the shapes of the features it depicts remain faithful to reality. Equidistant maps, on the other hand, show distances to scale correctly, while on an azimuthal projection, bearings are preserved. In all these cases, accuracy is achieved in one property at the expense of distortion in one or more of all the others.
For normal forecasting purposes, meteorologists like to use a polar stereographic projection. This is based on an imaginary plane intersecting the globe at a standard parallel onto which the lines of longitude and latitude are projected. The resulting map is both azimuthal and conformal, the former being particularly useful when plotting wind directions, and for analysing the relationship between isobars and winds.
Climatologists, however, have very different needs. For them, the relative size of a drought-stricken area, or of regions where temperatures may be above a certain threshold, are more important than precise angles and wind directions. For that reason, they prefer an equal area projection.