Choropleth map
Description
A choropleth map is a type of thematic map in which areas are shaded or patterned according to a data variable. The variable is categorized into intervals, with each interval represented by a colour, and the map filled accordingly. Colour progression is used to represent the differences, often blending from dark to light or one colour to another. The choropleth map provides an easy way to show how a measurement varies across a geographic area, or the level of variability within a region.
When to use
Choropleth maps are great to show geographical patterns in the data. If the data doesn’t show a clear geographical pattern, consider another chart type for the data. Choropleth maps work best when geographic regions are fairly consistent in size. Otherwise, larger areas appear more emphasized, which could result in misinterpretation.
Dos and donts
Make sure the legend is present.
Limit the steps of progression that are easily distinguishable by the human eye in order to make the map easy to read.
- Make sure to use normalized values (population per square kilometre) instead of raw data values (raw population figure) to show population density.
- Don’t use choropleth maps for accurate comparison of the values.
- Make sure to use the right colour scheme for your data, using a sequential colour scheme to drive the attention to higher values. Use a diverging scheme to drive the attention to both extremes of the scale.
Tools available
Power BI Illustrator GIS R D3.js
Bubble map
Description
As a variation of a bubble chart, bubble maps display bubbles over geographical regions rather than the cartesian plane. The size or area of the bubble indicates the value of the particular variable, with the position on the map indicating location. Bubble maps are useful for comparing proportions against geographic regions without the issues caused by the size of different areas, as you would have in choropleth maps.
When to use
The bubble map can be effective when analyzing and comparing a particular variable by geographical location. For example, displaying the number of refugees by country of asylum on a bubble map can provide useful insights on international displacement.
Dos and donts
Avoid having too many bubbles overlap on the map, which will make the comparison between bubbles difficult. Grouping data ranges into specifically sized bubbles or tying with another chart type can be an alternative.
Apply transparency to the colour of bubbles.
Make sure the legend is present.
Make sure the size of bubbles is mapped to its area, not to its radius.
Tools available
Power BI Illustrator GIS R D3.js
Flow map
Description
Flow maps show the flow of objects from one geographical location to another and their quantity. The arrows show direction, while the width illustrates the quantity. This helps to show how objects move geographically.
When to use
Flow maps are most frequently used to show the movement of population, but also animal migrations, money flow, the traffic of goods, etc.
Dos and donts
Use curved lines to show movement instead of straight lines.
Use headed arrows.
Make the arrows’ width proportional to flow rate.
Make sure flows and arrowheads don’t overlap.
Tools available
Illustrator GIS
Icon map
Description
Icon maps use icons to show geographical locations over a map. The shape or colour of the icon indicates the value of the particular variable, with the position on the map indicating location.
When to use
Icon maps can be used for indicating different kinds of geographical locations on the map such as cities, offices, ports, etc.
Dos and donts
Avoid overlapping symbols that make the map difficult to read.
Make sure the legend is present.
Tools available
Power BI Illustrator GIS
Dot density map
Description
A dot density map, also called dot map, uses dots to show spatial patterns or the distribution of data by placing equally sized points over a geographical region. Different shapes can also be used on a single map to indicate additional information.
When to use
Dot Maps can be used to show how things are distributed over a geographical region and give an overview of the data. It will provide useful information based on the pattern of clusters formed.
Dos and donts
Apply transparency to the dots.
- Don’t use dot density maps to show exact values.
Tools available
GIS
Pie chart map
Description
Pie chart maps are basically a combination of a map and a pie chart. It is used to visualize the location and numerical proportion in a simple way.
When to use
Pie chart maps are used to show the proportion of categorical data together with their geographical locations. One more variable can be further added to the visualization by assigning values to the size of the pie chart circle.
Dos and donts
Make sure the legend is present.