There are plenty of visualization methods available for organizing and displaying data. Depending on the type of data, you can choose which visual aid will best represent it. A spatial distribution, for example, can be conveniently displayed in a thematic map. If this map is used, methodology and map type must also be selected.
The purpose of a thematic map is not to navigate a terrain or an area but to coherently visualize specific data.
This article created by our team at MapSVG (the best WordPress map plugin) describes ten of the most popular thematic map types.
What Is a Thematic Map
A thematic map visualizes data related to a specific subject. Most people are familiar with navigation maps, used for orientation, and getting from A to B. Many people use them, such as car and taxi drivers, pilots, and tourists. Navigation maps show terrain features, such as coastlines, elevations, and roadways.
Thematic maps do not focus on the landscape or roadways of an area. They use a base map of the area, with the thematic overlay superimposed on it. The result is that information related to a particular question is spatially represented. It gives a geographical visualization of the data.
A thematic map is an efficient way of conveying information. Another reason for using this is that it is visually pleasing. Including a colorful map in a presentation will make it more attractive and will intrigue the audience.
The decision of which kind of map to use depends on two factors:
- Type of data
- Goal of the presentation
Knowledge of the different forms and styles of maps is indispensable to be able to consider both factors
The Best Types of Thematic Maps
In a choropleth map, geographic areas are colored, patterned, or shaded based on a value or interval. Data is delineated by a political or administrative boundary, by zip code, and so on. The relevant data is then compiled for that area.
A choropleth map is the map of choice when wanting to show how a certain variable changes over a geographical or geopolitical area.
This technique is handy in displaying the total number of votes for a political party by United States counties or by state. This is shown as an example below. Different colors can be used to indicate discrete values or attributes. The weight of the value can also be indicated by using lighter and darker shades.
The data should be discrete, standardized, and evenly distributed across the areal units.
This technique shows continuous data in a contour map. Contours are lines that are drawn on a map between points with equal value. Common applications of the isopleth maps are to display pollution or weather information.
The organization of the data in an isopleth map is not restricted to grouping in a predefined area unit, such as city districts. In this sense, the isopleth and choropleth maps are different. The differences are
- Isolines delimit areas with similar values. Isoline connects locations with the same value.
- Colors or patterns indicate areas with the same value or range.
This representation is effective in depicting spatial patterns, showing continuous patterns as opposed to discrete values and areas.
A drawback of isopleths is that they are not suited for discrete data. Displaying patchy distributions will look messy and cluttered. Another disadvantage is that much data is required to draw an accurate map.
Point maps are very uncomplicated and useful for visualizing data with a large geographical spread.
Even if data is spread out over a large area, a point map can display the information in a detailed way. The magnitude of the values is shown with smaller and larger sized dots on a map. The data on the map is shown as individual points rather than totaled over a specified area. For tallied geographic data, it is best to use the choropleth map.
An international company with various sites could use these maps to envision a certain variable for each of the locations. The point representation gives a quick and accurate overview.
The dasymetric map is a derivative of the choropleth map. In addition to the color-coded information, certain geographical information is given.
One criterion for the choropleth is that the data must be evenly distributed over the specifications. Often this is not the case, such as for population distribution. A second dasymetric map can be used to show urban areas, providing more detail, and facilitating interpretation.
Dot Distribution Maps
In a dot distribution map, dots are scattered over an area to indicate the presence or absence of a specific variable.
A higher dot density means a higher occurrence. Seen over a larger area, it reveals a spatial pattern and relative density. The user can define whether one dot represents single or multiple occurrences.
In a dot map, one dot is assigned per counting area, representing a specific number. In using dots, this map is similar to a point map. However, there are two differences. In a dot map, each dot represents more than one entity. Also, the number and position of the dots represent the distribution, not the exact location.
This map type is most suited for count data. By using different colors, multiple datasets can be displayed in a single chart.
Graduated Symbol Maps
In this map, symbols are used to indicate data. Their relative size is proportional to the values in the dataset.
Graduated symbol maps can be used instead of choropleths. Whereas the choropleth map has different colors and shades, the graduated map uses symbols. The data is usually expressed in an area and then converted to a standardized point with a proportional area. This map is more suited to display relative quantities rather than densities.
Some geographical information is lost when dots of various sizes are drawn onto it. Cities and areas are covered by dots that do not represent the surface area. However, enough geographical information can usually be gleaned from the underlying map. Besides that, the circles represent regional trends.
This data representation method works best when there is a large distribution and variation in the data. The meaning of the symbols is a relative magnitude of the events over different, spread-out sites.
The line map is seldom used because drawing them is laborious. It is a special representation where both location and time can be displayed simultaneously. Accordingly, it is useful in the analysis of some special scenarios. including bus routes, taxi routes, and subway lines.
Heat maps are often used to show weather impact and effect, or for mapping other natural phenomena. These phenomena are not bound by geographical or geopolitical limitations. To create a continuous heat surface, the discrete, localized points are interpolated. The results are visualized by using a color scale to illustrate the event density in that area.
Heat Point Maps
The heat point map is a hybrid between the heat and the point map. The heat point map uses a higher definition than the heat map. The points utilized in this kind of representation are circular. The circles are of the same size and overlap, giving a more layered appearance.
A heat point map can be implemented when the weight of each complex must be visualized within the geographical context.
The most common use of the flow map is when the relationship between origin and destination is to be mapped. Origins and destinations are displayed as points or surfaces. The relationship between the points or surfaces is shown by drawing lines between them. The color or width of the line shows the flow direction. Each point or surface can represent an origin, a destination, or both.
3D Extrusion Maps
The previous nine maps are all two-dimensional representations. A third dimension can be added to display data, for example, to represent elevation. This thematic map is called a 3D extrusion map.
Extrusions use attribute data to increase the height of 2D polygons. In other words, an additional attribute is chosen to be represented on a Z-axis. Using mapping software, like Mapbox, 3D visualizations can be added to a map. The added layer contains the specific height and base of the individual polygons.
3D extrusion maps invite interactive applications. The peaks on the maps can obscure the graph parts behind it. An interactive map allows for zooming and rotating so that all parts can be explored.
Ending thoughts on thematic maps
This article reviewed ten of the most often used thematic maps.
Thematic maps must always have a purpose, often related to presenting the spatial distribution of one or more phenomena, for example, understanding changing U.S. demographics. Additionally, thematic maps carry a decision-making purpose, like a real-time traffic map that helps travelers make decisions about the fastest route to take.
Understanding the aim of the chart or map is necessary for selecting the most effective visualization technique.
If you liked this article about thematic maps, you should also check out this article with map illustration examples.
We also wrote about a few related subjects like the map elements, map vector, what is a vector map, interactive maps, the choropleth map and how to make one, statistical maps, and all the types of maps out there.
I take it you like maps as well so make sure to check out MapSVG, a great WordPress map plugin you should check out.