A map is a symbolic representation of selected features of a place, typically drawn on a flat surface to communicate geographic information visually. Cartographers create these representations to show the shapes, sizes, locations, and distances between features. Since a single map cannot contain all information about an area, maps are classified based on their specific purpose and the data they display. This classification helps users quickly identify the map type suitable for their needs.
General Reference Maps
Reference maps are designed to show the location of various geographic features, serving as a foundational layer for understanding an area’s layout. These maps are not focused on a single theme but instead display a variety of natural and human-made features. They are categorized into two main subtypes: political and physical maps.
Political maps are among the most recognizable reference maps, illustrating human-defined boundaries between governmental units such as countries, states, and counties. They use distinct colors and lines to delineate these administrative divisions, often including labels for major cities, capitals, and primary transportation networks. The function of a political map is to help people understand the geopolitical structure and organization of a territory.
Physical maps, in contrast, focus on the natural landscape features of the Earth, frequently referred to as relief maps. They use color schemes and shading to show elevation and landforms, such as mountains, valleys, plains, and bodies of water. Colors often follow conventions: green for low-lying areas, tans and browns for increasing elevation, and blue shades for water depth. While their focus is natural geography, physical maps often include major political boundaries or cities for geographic context.
Thematic Maps
Thematic maps are designed to visualize the spatial distribution of one or more particular attributes, or themes, across a geographic region. Unlike general reference maps that show location, the content of a thematic map is the data itself, which might be qualitative or quantitative. These maps are tools for understanding spatial patterns and trends in data, such as population density, climate zones, or income distribution.
One common type is the Choropleth map, which uses color shading or patterns to represent data values in pre-defined geographic areas, like states or counties. Darker colors indicate higher values or densities, making it easy to compare statistics across different regions. This method is effective for displaying derived values, such as rates or percentages, rather than absolute counts.
Isoline maps use continuous lines, called isolines, to connect points that have an equal value of a specific variable. For instance, weather maps frequently use isobars to connect points of equal atmospheric pressure or isotherms to connect points of equal temperature. Dot Density maps are another technique, where each dot placed within an area represents a specific quantity of the measured variable, which visually conveys the phenomenon’s spatial concentration and distribution.
Topographic and Terrain Maps
Topographic maps represent a specialized form of reference map, dedicated to accurately depicting the three-dimensional characteristics of the Earth’s surface on a two-dimensional plane. Their purpose is to show terrain shape and elevation, achieved through the use of contour lines. This level of detail is necessary for activities like engineering, land surveying, and backcountry navigation.
A contour line is an imaginary line connecting all points on the map that share the exact same elevation above a fixed datum, such as mean sea level. The interval, or vertical distance, between successive contour lines is constant across the map, allowing for consistent measurement of elevation change.
The spacing of these lines indicates the steepness of the terrain. Contour lines that are drawn close together show a steep slope, because the elevation changes rapidly over a short horizontal distance. Conversely, lines that are far apart represent a gentle slope or relatively flat terrain. Topographic maps also include other detailed features, such as human-made structures, roads, and water bodies, providing a comprehensive view of the landscape.
Navigational and Route Maps
Navigational maps facilitate movement, allowing the user to plot and follow a course safely and efficiently. These maps prioritize accurate direction and distance, often requiring specialized map projections tailored to the medium of travel. They are dynamic tools that help users account for movement and potential hazards.
Nautical charts are designed for marine navigation, providing essential information for watercraft, such as water depths, submerged obstacles, and the locations of aids to navigation. Aeronautical charts are used by pilots, emphasizing elements like airspace boundaries, minimum safe altitudes, and the location of airports and radio aids.
Road and street maps focus on terrestrial connectivity, highlighting highways, secondary roads, and city streets. These maps prioritize ease of route-finding and may simplify geographical features to make the transportation network clearer for drivers. All navigational maps share the goal of providing the specialized information required to get from a starting point to a destination.