Drawing Lines On Maps With Power Map And Power Query

Recently, I was working with a customer that wanted to be able to draw lines between two points in Power Map. At the time I thought the only way that it might be possible was by using Power Query to generate a table of data containing a series of points that were so close together that they looked like a single line, and then plot these points in Power Map (similar to what I show in the screenshot here). Soon after, the new custom regions functionality was released in Power Map (there’s no documentation I can find right now, but this blog post is reasonably detailed) and I wondered whether now it might be possible to draw lines. Unfortunately not: Power Map can now import SHP and KML files, but it doesn’t support all the features of KML – only polygons (and even then not all the features of polygons, although inner and outer boundaries work fine). I guess this is ok for the primary use-case of Power Map, which is plotting BI data on a map, but it would be nice to see more KML features supported so that Power Map can show richer supporting information for the data: things like arrows showing direction of travel, and so on.

Anyway, I then thought – why not use polygons to draw these lines? Again, I hit a slight problem: I wanted to generate the polygons for the lines in code, and Power Map can only import SHP or KML data from files. It would be really useful if we could use shape data stored in the Excel Data Model… but we can’t. However, it is possible to use Power Query to generate KML and then copy and paste this code into a file, which can then be imported into Power Map. So, just for the fun of it, I put together a proof-of-concept workbook containing Power Query queries to generate all the tables and KML code needed to draw lines between two places, and a Power Map tour that shows the output. Here’s what the end result looks like:

You can download my example workbook that contains all the code, plus all the supporting files, here. You will need to update some file paths in the M code to get it all to work.

The starting point is two tables on the worksheet, one containing the single starting point for the lines, the other all of the destinations:

There’s a lot of M code so I’m not going to include it in this post, but here’s an overview of what each query does:

• GetLatLong is a function that calls the Bing Maps REST API to find the latitude and longitude for each place in the tables above. You will need your own Bing Maps account key if you want to use this code yourself – you can get one at https://www.bingmapsportal.com/
• Starting Point and Ending Points simply load the data from the Excel tables
• StartingPointLatLong gets the latitude and longitude of the starting point by calling GetLatLong
• StartEndPoints gets the latitude and longitude of all the ending points by calling GetLatLong, adds custom columns to show the starting point name, latitude and longitude against each ending point, and loads the result to the Excel Data Model. You have to have some data in the Excel Data Model for Power Map to display the lines, and it’s important that Power Map can match the values in one column in this table with the names of objects in the KML file.
• BasicPolygonTemplate loads a fragment of KML, containing the definition of a polygon, from a text file. This contains two ‘parameters’, @Name and @Coordinates, which will be overwritten using Text.Replace() later on when the actual KML is being generated.
• GetCoordinateList is a function to draw a rectangular polygon that represents the line between the starting point and an ending point. I had a lot of fun trying to get the code for this working properly (I wish I could remember any of the trigonometry that I learned after the age of 13…) and I’m still not convinced the rectangles are properly rectangular, but they’re good enough.
• KML generates the KML for all of the polygons. The output of this query must be copied from the Power Query query window into a text file with the .kml extension, for example Test.kml. There’s no need to load the output of this query to anywhere.

With all of that done, you now need to open Power Map and create a new tour. Choose EndingPoint as the sole Geography column, then choose Custom Region (.kml, .shp) from the dropdown list below and click Yes to import custom regions.

Select the .kml file you created earlier, containing the output of the KML Power Query query, and then click Import:

Finally, change the visualisation type to Region and optionally add Ending Point to Category to make the lines different colours:

And bingo, you see the lines:

Support for custom regions is a massive step forward for Power Map in my opinion: rather than just being a toy for creating flashy demos it’s now able to handle a lot more real-world requirements. However, having some way of programmatically creating regions and shapes (either through Power Query as I’ve done here, or using VBA or some other API), being able to load shape data from the Excel Data Model, or even just to be able to draw shapes on a map manually, would be welcome. I’m no mapping expert but I’ve come across a few frustrated Mappoint (which was discontinued at the end of 2014) users who would like to use Power Map but find that it can’t do everything that they need. The code in this post shows what’s possible but it’s still way too complex for most users and hardly an elegant solution.