Thematic maps: the eight types, with examples and when to use each
Most map types are easy to name and hard to choose between. This guide covers what a thematic map actually is, the eight types you will meet in practice, the data each one suits, and the four mistakes that quietly turn a good-looking map into a misleading one.
A thematic map is a map that shows the distribution of a single subject — population, income, sales, rainfall — across a geographic area, rather than showing the geography itself. Where a reference map answers “where is it,” a thematic map answers “how much of it is here, and where is there more.”
Thematic maps vs reference maps
The distinction is about purpose, not appearance. A reference map is a general-purpose picture of a place: roads, borders, rivers and place names, all given roughly equal weight. A road atlas or a political world map is a reference map. Nothing is being argued.
A thematic map has an argument. It picks one variable and subordinates everything else to showing how that variable varies across space. Boundaries and coastlines are still there, but only as scaffolding — they exist so you can locate the pattern, not because the map is about them. That is why a thematic map can drop detail a reference map would never omit: if it does not help you read the theme, it is noise.
The practical consequence is that thematic maps can be wrong in ways reference maps cannot. A reference map is either accurate or inaccurate. A thematic map can be perfectly accurate and still mislead, because the choices made in turning numbers into colours — which classes, which palette, which denominator — change what the reader concludes. Much of this guide is about those choices.
The eight types of thematic map
Cartography textbooks disagree on the exact list, and some of these overlap. This is the practical set — the ones you will actually be asked to produce or interpret.
1 · Choropleth map
Predefined areas — countries, states, counties, ZIP codes — shaded by the value of a variable. The most common thematic map by a wide margin, and the easiest to get wrong.
Use for: rates, ratios, densities and percentages. Unemployment rate, sales per rep, households per square mile.Avoid for: raw counts. A choropleth of total sales just draws a map of where the big areas are.
2 · Graduated symbol map
A symbol, usually a circle, placed on each location and sized in proportion to its value. Because the symbol carries the magnitude, the area underneath cannot distort it.
Use for: raw totals, and any time area size would mislead. City populations, revenue by branch, accounts per territory.Avoid for: dense point sets where symbols overlap into an unreadable blob.
3 · Dot density map
Each dot represents a fixed quantity — one dot per 100 people, per 10 accounts — scattered within the area it belongs to. The eye reads concentration directly.
Use for: showing distribution and clustering within areas, and comparing absolute quantities across uneven geography.Avoid when: readers may take dot placement literally. Dots are usually placed randomly inside the area, not at real addresses.
4 · Heat map
A continuous colour surface calculated from point density, so intensity fades smoothly rather than stopping at a boundary. Closely related to the isopleth map, which draws contour lines through equal values.
Use for: spotting concentrations when the underlying boundaries are irrelevant or arbitrary.Avoid for: anything requiring an exact figure. Heat maps show shape, not quantity.
5 · Cluster map
Strictly a rendering technique rather than a classical thematic type: nearby points are collapsed into a single numbered symbol so a dense map stays legible, and the clusters split apart as you zoom in.
Use for: plotting thousands of individual records — customers, stores, service calls — without a solid mass of overlapping pins.Avoid when: the exact count in a small area matters, since the number shown depends on the zoom level.
6 · Cartogram
Geography itself is distorted so that each area’s size reflects its value rather than its land area. Election maps use these to stop empty countryside from visually outvoting cities.
Use for: making the point that population or value is distributed very differently from land.Avoid when: the audience needs to recognise the geography, which distortion actively prevents.
7 · Bivariate and over-under maps
Two variables shown at once — either blended into a two-dimensional colour scheme, or simplified into a comparison against a target so each area reads as above or below.
Use for: relationships and gaps. Potential against coverage; actual against quota; workload against headcount.Avoid when: the audience is general. Full bivariate legends are hard to read, which is exactly why the over-under simplification exists.
8 · Flow map
Lines or arrows connecting origins to destinations, usually with the line weight scaled to the volume moving along it.
Use for: movement between places. Shipments, migration, referral patterns, drive routes.Avoid when: there are many origins and many destinations — flow maps turn into spaghetti fast.
Which type should you use?
Start with the shape of your data rather than the look of the map. In almost every case the data dictates the answer.
| What you have | Use this | Why |
|---|---|---|
| A rate, ratio or percentage by area | Choropleth | Already normalised, so shading is honest |
| A raw total by area | Graduated symbol | Symbol size carries magnitude; area size cannot distort it |
| A raw total you want to show within areas | Dot density | Reveals concentration that a single shade would flatten |
| Thousands of individual points | Cluster map | Keeps the map legible at every zoom level |
| Points whose boundaries do not matter | Heat map | Concentration reads through arbitrary borders |
| Two variables that interact | Bivariate | Shows the relationship, not two separate maps |
| Performance against a target | Over-under | Reduces two numbers to one clear verdict per area |
| Value distributed unlike land area | Cartogram | Stops empty space dominating the picture |
| Movement between places | Flow map | Only type that shows direction and volume together |
Four mistakes that make thematic maps lie
Every one of these produces a map that looks professional and tells you something untrue. They are worth knowing whether you are making maps or being shown them.
1 · Shading raw counts on a choropleth
The classic error, and the most common. Shade US states by total sales and you will produce, almost exactly, a map of state population — California and Texas dark, Wyoming pale — no matter what your sales actually did. The fix is to normalise: sales per capita, per account, per rep, per square mile. If you cannot divide it by something, a choropleth is the wrong map and you want graduated symbols.
2 · Letting the class breaks pick the story
The same data split into equal intervals, quantiles, or natural breaks produces three maps that look meaningfully different. None is wrong, but the choice determines which areas appear alarming. Quantiles guarantee an even spread of colour and can manufacture contrast where there is almost none; equal intervals do the reverse and can hide real variation when the data is skewed. State the method in the legend, and check the map against the raw distribution before you publish it.
3 · Rainbow colour ramps
A red-through-green rainbow has no perceptual order — nothing tells the eye that green is more than yellow — and it is unreadable for the roughly 8% of men with red-green colour vision deficiency. Sequential data wants a single hue running light to dark. Diverging data, where there is a meaningful midpoint such as a quota, wants two hues meeting at a neutral centre.
4 · Forgetting the boundaries are a choice
Cartographers call this the modifiable areal unit problem: the same underlying points, aggregated by ZIP code rather than county, can produce genuinely opposite-looking maps. It is not a bug you can fix, only one you can be aware of. If a pattern disappears when you change the aggregation level, it was probably an artefact of the boundaries rather than something real in the data.
Thematic maps in sales territory design
Territory design is one of the places thematic mapping earns its keep, because the whole job is spotting imbalance — and imbalance is exactly what a well-chosen thematic map makes visible in a second and a spreadsheet hides for a week. AlignMix builds three of the eight types above on any column you import, and the sections below walk through each one.
- Choropleths by territory or ZIP code turn any imported column — potential, penetration, growth, workload — into a balance check across the whole field force. Shading the ZIP codes rather than the territories is what you want when you are deciding where a boundary should go, rather than judging where it currently is.
- Bivariate thematic maps put two measures on the map at once, which is where territory design questions actually live. Potential against current coverage shows you where opportunity is going unworked; workload against headcount shows you where the next rep should go. A single-variable map can only ever answer half of either question.
- Over-under maps compress the same idea to a verdict: each territory is coloured by whether it sits above or below a target — a workload figure, a revenue quota, an account count. It is the map to bring to the meeting, because nobody has to read a legend to understand it.
- Hot Spots, the heat map overlay, shades concentrations of accounts, revenue or any imported metric, warm where activity is dense and cool where it thins out. Because it ignores boundaries, it finds both the pockets worth splitting and the coverage gaps that fall between territories and so never show up in a per-territory report.
Used together they answer the three questions a realignment turns on: where the business is, who is carrying too much of it, and where nobody is carrying it at all.
Go deeper: the tool-by-tool walkthrough covers Hot Spots, Over Under, ZIP code, territory and bi-variate thematic maps with video for each. There is also a focused guide to spotting over- and under-performing territories and one on ZIP code thematic mapping.
Common questions
What is a thematic map?
A thematic map shows how a single subject — population, income, sales, rainfall — is distributed across a geographic area, rather than showing the geography itself. A reference map answers “where is it.” A thematic map answers “how much of it is here, and where is there more.”
What are the main types of thematic map?
Eight cover almost every practical case: choropleth, graduated symbol, dot density, heat map, cluster map, cartogram, bivariate or over-under, and flow map. Choropleth is by far the most common, and graduated symbol is the one most often needed in its place.
What is the difference between a choropleth map and a heat map?
A choropleth shades predefined areas — states, counties, ZIP codes — so colour stops abruptly at each boundary. A heat map calculates a continuous surface from point density, so intensity fades smoothly and ignores boundaries entirely. Use a choropleth when the areas are meaningful, and a heat map when they are not.
Why should I not use raw numbers on a choropleth map?
Because larger areas collect larger totals regardless of the pattern you are trying to show. Shading states by total sales mostly reproduces a map of population. Normalise first — per capita, per account, per square mile — or switch to graduated symbols, which carry magnitude in the symbol rather than the area.
Is a heat map a thematic map?
Yes. A heat map is a thematic map that renders point density as a continuous colour surface. It belongs to the same family as the isopleth map, which draws contour lines through points of equal value rather than filling with colour.
What is a cluster map?
A map that groups nearby points into a single numbered symbol so dense areas stay readable, splitting apart as you zoom in. It is a legibility technique rather than a classical thematic type — the number shown depends on the zoom level, so it is for seeing where records concentrate, not for reading exact counts.
Can territory mapping software build thematic maps?
Yes, and it is one of the main reasons to use purpose-built territory software rather than a general mapping tool. AlignMix builds single-variable and bivariate thematic maps, over-under maps that colour territories against a target, and Hot Spots heat map overlays — all from a spreadsheet import, on all 41,633 US ZIP codes plus international geographies.
See thematic maps on your own data
AlignMix builds over-under maps, Hot Spots and ZIP code thematic maps from a spreadsheet import, across all 41,633 US ZIP codes plus international geographies. There is a two-week free trial and no demo is required first.
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Related: sales territory mapping software · territory management · glossary of mapping terms · geographic data coverage