The commonest maps are those containing data on the relief. Thematic maps focus on a specific topic, like temperature or rainfall.
To be valid, maps are permanently revised, to reflect changes that may occur, like newly built roads or building demolitions. These details are essential for defining borders, from small properties to countries. When borders changes, maps must be updated. At the beginning of the '90s, with the collapse of the USSR, mappers had to make new maps of Eastern Europe and ex-USSR.
Geographic maps. Atlases contain general maps of the world, with thematic maps displaying population distribution or economic resources. Political maps present borders, national or regional, with the names of the political or administrative units, their capitals and the main cities. Colors are used to make the distinction between administrative units, like countries or counties.
Physical maps present various forms of relief. In this case, the mappers use bench marks or colors to represent the altitude, from green for lowlands to red and white for the highest mountains. Other techniques, like hatching the hills or using model photos of the relief, confer a tridimensional impression of the mountains, hills and valleys. The height of the mountain peaks can be marked.
Topographic maps do not come with information on the terrain (relief or hydrologic distribution) only, but also with data on population, like human settlements, overlapped onto the natural relief forms. Topographic maps are useful for the travelers, regardless they walk on foot or ride a bike or motorcycle. They contain valuable information for geographers and projectors. Many governments have cartography departments, making maps of the whole territory of the country at a scale of 1:50,000 (1 cm means 500 m or 1,660 ft on the field). This scale offers a lot of details. Relief forms are represented through contours, usually brown lines which bind places of the same height. Topographic maps can be also used in sports, like field orientation and navigation.
Thematic maps cover many topics, from clime to population distribution or resource distribution. There are several types.
Isogram (isoline) maps bind places of equal value with lines. Meteorological and clime maps use these maps for presenting isotherms (for temperature), isobars (for atmosphere pressure) and isohyets (for rainfall).
The Urbanists use isoline maps for deciding, for example, the placement of a supermarket. In this case, they must know the probable number of future clients. For this purpose, they make isochrone maps, with lines that unite the places with the same displacement time to the proposed place. This way, the urbanists can estimate the number of persons located at a distance of 15, 30 or 45 minutes of the target place.
Many thematic maps use color symbols for expressing quantities. Some demographic maps use points for indicating regions of different population density. A congestion of points indicates a population concentration. Points located at great distances one from another show weakly populated regions.
Some colored maps use hues to represent the population density, birth rate or crime rate. Darker hues point to higher values. Maps with flow lines indicate movements, like trade changes or population migration. The thickness of the arrows points the degree of the phenomenon.
Topographic maps are highly stylized. The map of a railway or bus network must not be represented on real scale or to be geographically correct, as these details could create confusions to the travelers. The travelers need simple diagrams of the routes and stations, like that of a metro system in a large city.
Cartograms are mathematic diagrams presenting geographic information, made to resemble maps. The people making the maps can represent the population of the countries of the world so that the surface of each country to correspond with its population. The shape of the countries represented in cartograms cannot correspond with their real shapes to make the continents follow their real contour. In catograms the accuracy of the shapes is less important than their statistical data.
Geological maps give information on the rocks existent at the surface of the Earth. They are used by the builders of buildings, roads or railways and by geology or geography lovers or prospectors as well. The geological maps are made on scales varying from 1:10,000 to 1: 250,000. Maps made at a scale of 1:50,000 can show the physical character and structure of the rocks, using colors and symbols. This way, they do not reveal only delimitations on the terrain but also the inclination of the rocks.
There are maps presenting the soil types, while geochemical maps represent concentrations of elements, like uranium, based on sediment probes taken from river beds. Maps representing the spread of human or animal diseases can help people discover the cause of their emergence.
Roads, rivers or railways cannot be represented at their real scale. For example, a map with a scale of 1:10,000 represent a road through a 2 mm wide line. In this case, the road would be 20 m (66 ft) wide in reality. 2 mm on a 1:50,000 map would translate through a 100 m (330 ft) wide road, while on a 1:250,000 map, this would mean a 500 m (1,660 ft) wide road. On scales smaller than 1:50,000, mappers cannot represent all the meanders or curbs of a road passing through a steep slope.
Maps smaller than 1:50,000 cannot detail the use of the land: they can represent only buildings or forests, but not metro ways or sewages.
Knowing to read maps can deliver a lot of information. The lack of drainage on a rainy area can point to a karst relief, where the water is drained into subterranean caves. Lines binding the springs can point the line delimiting an aquifer (a water-containing rock) and an impermeable layer, the stops the water run.
Nowadays, maps can be digitalized for simplifying their representation. This way, they can be updated easier and more rapidly.
Today, the GPS (Global Positioning System) can be combined with GIS (Geographical Information Services) to successfully guide soldiers and missiles, but also they can be applied for projecting sewage systems or to monitor the changes in the population structure. These systems could make possible the computerized navigation. A GPS system connected to a digitalized data base of maps not only could offer information on the location of the driver, but deliver a route to follow to the destination as well.