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One of the most powerful ways to visualise data is spatially. Used appropriately, map-based data visualisations can make otherwise-invisible connections obvious, bringing your data to life in a very immediate and visually-compelling way.
This kind of visualisation has long been difficult to create, needing expensive and complex software. Fortunately, Power BI now offers two easy-to-use map visualisations that bring this capability within anyone’s reach.
The map visualisations in Power BI can work with various different kinds of geographical data, from place names and postal codes to precise latitudes and longitudes. If your data has latitude and longitude data, this is the best option (since it’s completely unambiguous), but Microsoft offers a number of tricks you can use to improve the recognition of your geographical data.
The simplest and most versatile map visualisation is the Basic Map, also known as Bubble Map. This visualisation places circular markers for each data point on a standard map.
The simplest way to use this visualisation is to show locations divided into different categories. For example, this visualisation shows the locations of different types of tree in Camden, London (this data comes from the excellent Open Data Camden project).
Any additional data associated with each location can be shown in several different ways, depending on how your data is structured. If you have just a single value for each location, that can be used to determine the size of the marker.
Here is the same visualisation, but with the markers sized according to the height of each tree.
If you have several categories of data for each location, you can display them as pie charts. Here is an example (using made-up data) showing visitor numbers at three locations, broken down by ticket type:
The overall size of each marker shows the total of all categories, while the pie chart within the marker shows the category breakdown.
Finally, you can visualise two different data values per marker by using one to set the size of the marker, and the other to set the colour saturation. However, you cannot combine this with any categorisation. For example, we can show both total visitors (size) and total sales (saturation) at each of our locations like this:
The other standard map visualisation available in Power BI is the Filled Map (also known as a choropleth). This type of map shows regions filled with colour, with the colour saturation representing the value.
Making effective use of the Filled Map visualisation is a little more difficult than the Basic Map. The available regions are limited to those that Bing Maps can understand, and their geographic coverage sometimes leaves a little to be desired, especially outside the USA. It also becomes tricky if you move away from the standard Country/Region/State/County model. So, for example, you can’t use parliamentary constituencies as your regions, because they don’t fit Bing’s default geographical model.
There are a couple of other map visualisation options available, but these are currently only in preview, so I won’t go into them in too much depth. Preview features need to be manually enabled within Power BI.
Shape Maps are broadly similar to Filled Maps, but let you choose different pre-defined maps (such as US states or the counties of Ireland) as the base map. There is also the promise that Shape Maps will offer the ability to define custom areas using TopoJSON code when the feature comes out of preview.
The ArcGIS Map visualisation is supplied by Esri, one of the leaders in the field of Geographical Information Systems (GIS). It lets you select from several different base maps, and apply different “reference layers” as overlays. As well as letting you plot location points of varying sizes (like the Basic Map), you can also show your data as a heat map, or as counts of values within regions.
Want to get started with Power BI? Check out our previous blog post, which helps you get hands-on with the app.
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