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MapInfo Monday: Thematic Map with Different Ranges

  • 1.  MapInfo Monday: Thematic Map with Different Ranges

    Posted 12-23-2024 04:00

    During the month of November I undertook the #30DayMapChallenge where a different map was created every day following a specific theme, having been a MapInfo Pro user for more than 20 years I used MapInfo Pro for the majority of these maps.  Following this @Peter Møller asked me to contribute to #MapInfoMonday using some of these maps as a basis for some articles.  Today’s article focuses on thematic mapping and how the same data can be presented differently and how this may change how your map is interpreted.  To see the original post on LinkedIn please take a look at #30DayMapChallenge

    The data used for these maps came from the National Chargepoint Registry (NCR) which is a database of publicly available chargepoints for electric vehicles (EV) in the UK established in 2011.  The data used in these maps can  be found here.

    The database provided the postcode of each publicly available EV chargepoint and was imported into MapInfo Pro, these were geocoded using Ordnance Survey CodePoint OpenData.  Some postcodes had multiple chargepoints, therefore the data was grouped by postcode and the count of postcodes calculated and a thematic layer was added to the map.

    What does this map tell us? It clearly shows that there are a higher number of Chargepoints in urban areas – which is pretty obvious – but it also shows that across England, Scotland and Wales there is a good distribution of Chargepoints even in more rural areas perhaps reducing the “range anxiety” that some motorists felt when first purchasing electric vehicles. However mapping the locations of individual charges doesn’t give a full picture. 

    The NCR data was grouped again into postcode districts to establish the distribution of EV chargepoints by region.  The postcode district boundaries used in these maps was derived by creating Voronoi polygons of OS CodePoint OpenData.  To learn more about creating Voronoi polygons please refer to this article - MapInfo Monday: Creating Voronoi Polygons from Points | MapInfo Pro.

    In the map below the ranges used for the thematic map are the same as the map showing the individual locations above. The top range (i.e. the districts that have the most chargers) is 5+. Obviously there are a lot of postcode districts that have more than 5 Chargepoints within them and using 5+ as the top range is quite misleading as it suggests that the distribution of Chargepoints is fairly consistent across the South East. Clearly this map is not very useful and the ranges need to be changed to give the map more meaning.

    Modify a thematic map

    To modify a thematic map click on the thematic map icon circled red in the image below to bring up the “Modify Thematic Map” dialog. 

    Click on the customize ranges button (circled green) to open the “Customize Ranges” dialog.  You can see that 64% of the postcode districts fall in to the top range.

    In the dropdown menu change the method to “Equal Count”.

    Click on the “Recalc” button (circled red) and the ranges are recalculated:

    You can now see that the percentage distribution of postcode districts is now more equal with approximately 20% of postcode districts in each range.  The resulting map is shown below.  It is now possible to see a greater range of variation in the distribution of EV chargers in the South East of England.
    An alternative way to customise the ranges for a thematic map is to use the Calculate Method on the Theme tab.  The theme tab is a contextual tab which becomes available when the thematic layer is highlighted in the Explorer.

    Although the second map reflects the distribution of EV chargers much more clearly than the first I still wasn’t convinced that the map was very useful!  The number of EV chargers in a particular region doesn’t really explain how well served that region is unless you take into account the number of people that might be able to access them.  Therefore for the final map in the series I used Royal Mail PAF data to count the number of addresses in each postcode district and using SQL select calculated the number of addresses (used as a proxy for households) each EV charger served.  The resulting map looked like this:
    As you can see it shows that the area just North of Brighton is just as well served as London but you couldn’t see this in the second map when simply the number of EV chargers was counted.  The other point to note about this final map is that the legend is reversed as the higher the number of addresses served by an EV charger is the worse that area is provided for so it was important to “flip” the ranges.

    Theme Templates and Styles

    During the creation of these maps I wanted the theme to be consistent across all the maps and therefore once I had decided on the colour scheme I saved it as a template in order that it was available to use on subsequent maps.  This can be done by clicking on the “Save As…” button in the “Modify Thematic Map” dialog as shown in the image below:

    Next time you create a thematic map, in this case a “Regions Ranges” thematic map the theme will be in the list available to you:

    If we modify the ranges again by doubling the number and you are using the same template MapInfo Pro will assign the top theme to the top 6 ranges which if you clicked ok would just result in the map looking exactly the same!  This time click on the “Styles” button:

    Then highlight the “color” option in the Auto Spread section.  This will spread the colour of your lowest range and the highest range across all ten ranges:

    Happy #MapInfoMonday








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    Louise Kavanagh
    Director
    Apogee Data Consulting Ltd
    Tenterden
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