The main types of maps are political, physical, topographic, road, cadastral, climate, weather, geologic, choropleth, dot density, proportional symbol, isoline, flow maps, cartograms, and nautical and aeronautical charts. Cartographers sort them into two families. General reference maps show where things are: borders, rivers, roads, property lines. Thematic maps show how one subject, such as rainfall, population or votes, varies from place to place. Navigation charts for ships and aircraft are specialised reference maps, built to be used while moving.
What follows takes each type in turn, grouped by the question it answers, with the details that tell one type from another.
Reference Maps and Thematic Maps: The Basic Split
A reference map tries to show many kinds of features together, as accurately as its scale allows. A national atlas page with borders, cities, rivers and relief is the classic example. A thematic map deliberately leaves out almost everything except one variable and a faint base map for orientation. The distinction matters because it tells you what a map is good for. You can find a road on a reference map. You should not try to read exact distances off a thematic map of income, where the geography is only there to hold the data.
Maps That Show Where Things Are
Political maps show the boundaries of countries, states and provinces, usually by colouring each unit differently and marking capitals with a star. The colours carry no meaning in themselves. Mapmakers only need adjacent units to differ, and the four colour theorem, proved in 1976, shows that four colours are always enough on a flat plane. Political maps date quickly: South Sudan's independence in 2011 and Eswatini's renaming in 2018 each made a generation of wall maps out of date.
Physical maps show the land itself: mountains, plains, rivers, lakes and deserts. Most use hypsometric tinting, a colour scale running from green lowlands through yellow and brown to white peaks. That convention misleads some readers, because green means low, not fertile. Death Valley would be coloured green and the Tibetan Plateau brown, although neither is anything like the colour suggests.
Road maps are reference maps edited for drivers: highway numbers, interchanges, distances and fuel stops, with terrain reduced or removed. Digital road maps have mostly replaced the folded kind, but the data underneath is the same. Every junction, turn restriction and speed limit has to be recorded, which is why services such as Google Maps and OpenStreetMap depend on constant updates.
Cadastral maps show land ownership: the boundary of each parcel, its reference number and sometimes its value for tax purposes. They are the least glamorous maps and among the most legally important. The Domesday Book of 1086 was a written cadastre, and modern land registries still resolve disputes by the lines on these maps.
Topographic Maps and Contour Lines
A topographic map is a detailed reference map that also shows the shape of the ground, using contour lines. Each contour joins points at the same height above sea level. Lines packed close together mean a steep slope, widely spaced lines mean gentle ground, and a set of closed rings marks a hill or a depression. The vertical gap between neighbouring lines, the contour interval, is printed in the margin and varies with the terrain. It is typically 5 or 10 metres on a British Ordnance Survey Explorer sheet at 1:25,000, and 10, 20 or 40 feet on a US Geological Survey 7.5-minute quadrangle at 1:24,000.
The USGS mapped the whole lower 48 states at that scale, about 54,000 sheets, in a programme finished in 1992. Topographic maps are what hikers, engineers, soldiers and search-and-rescue teams actually use. Reading them depends on the legend, and the symbols are explained in our guide to map legends and keys.
Six Ways to Map a Number
Thematic maps come in several standard forms, and choosing the wrong one is the most common way a data map misleads.
Choropleth maps shade whole areas, such as countries or counties, by a value. They are easy to read and easy to misuse. A large, empty county draws the eye far more than a small, crowded one, so a choropleth of raw totals mainly shows where the big areas are. Good choropleths map rates, such as per person or per square kilometre, rather than counts.
Dot density maps place one dot for each fixed quantity, such as a thousand people, so clustering shows up directly. The most famous early dot map is John Snow's 1854 map of cholera deaths in Soho. It plotted each death as a mark by its house, and the cluster around the Broad Street water pump helped persuade the authorities to remove the pump's handle.
Proportional symbol maps scale a circle or other shape to the value at each place, which suits data tied to points, such as city populations or earthquake magnitudes.
Isoline maps draw lines through points of equal value. Contours are one kind. Others include isobars for air pressure, isotherms for temperature and isohyets for rainfall. Edmond Halley's 1701 chart of magnetic variation across the Atlantic is one of the first published isoline maps.
Flow maps show movement with lines whose width is proportional to the quantity moving. Charles Minard's 1869 map of Napoleon's 1812 Russian campaign is the best-known example. A band that starts 422,000 men wide at the Niemen River shrinks to 10,000 on the retreat, with the temperature plotted underneath.
Cartograms abandon true area and resize each country by a variable instead, such as population or GDP. On a population cartogram, India and China swell, while Russia, Canada and Australia shrink to slivers.
Climate, Weather and Rock
Climate maps show long-term averages rather than daily conditions. The standard world version is the Köppen classification, first published by Wladimir Köppen in 1884 and revised until the 1930s. It divides the land into five main groups (tropical, dry, temperate, continental and polar), coded by letters such as Af for tropical rainforest. Our explainer on the Köppen climate classification decodes every letter.
Weather maps show conditions at one moment: isobars, high and low pressure centres, and the blue-triangle and red-semicircle symbols for cold and warm fronts. Those front symbols come from the Bergen School of Norwegian meteorologists around 1919, who borrowed "front" from the First World War battle lines.
Geologic maps colour the ground by the rock beneath the soil and its age, with symbols for faults and the angle at which rock layers dip. William Smith's 1815 map of England and Wales was the first national geologic map. It was drawn largely from what he saw while surveying canals, and it is still recognisably accurate.
Charts for Ships and Aircraft
Navigators call their maps charts, and the difference is more than a name. A nautical chart shows water depths as numbered soundings, along with hazards, buoys, lights and the seabed, and it is published so that it can be corrected: mariners update paper charts by hand from weekly Notices to Mariners. Most charts use the Mercator projection, because on Mercator a line of constant compass bearing is straight, which makes steering by it simple.
Aeronautical charts do the same for pilots. US sectional charts, at 1:500,000, show airspace boundaries, radio frequencies, airports and the heights of obstacles such as masts, as well as terrain.
Digital Maps and GIS
Most maps today are made and read on screens, and that has changed how they are built rather than what types exist. A geographic information system, or GIS, stores each kind of feature as a separate layer: roads, rivers, parcels, elevation, census counts. The mapmaker then combines layers for each purpose. The same data can produce a road map, a cadastral map and a choropleth, which is why modern national mapping agencies such as Ordnance Survey maintain one master database instead of separate map series. The approach dates from the Canada Geographic Information System of the 1960s, built to inventory land use across rural Canada. Our introduction to GIS explains how the layers work.
Web maps add one more difference. They are stored as tiles at many zoom levels, so a single map can go from a whole continent to a street corner, changing from a small-scale reference map to a large-scale one on the way.
Why Every Flat Map Distorts Something
All the types above share one problem: the Earth is round and the map is flat, so every world map gets something wrong. A projection can keep shapes correct locally (conformal), keep areas correct (equal-area) or compromise between the two, but it cannot do both. Mercator's 1569 projection is conformal and makes Greenland look as large as Africa, which is about fourteen times its size. The Gall–Peters projection is equal-area and stretches the tropics. The Robinson (1963), Winkel tripel and Equal Earth (2018) projections compromise, which is why they are used for most world maps today. Each one is compared in our guide to map projections.
Scale causes the other common confusion. A large-scale map, such as 1:10,000, shows a small area in great detail. A small-scale map, such as 1:10,000,000, shows a large area with little detail. It sounds backwards until you think of the scale as a fraction: 1/10,000 is a larger number than 1/10,000,000.