In my recent post on web services in Power Query I mentioned that while the Power Query Web.Contents() function generates a GET request by default, you can make it generate a POST request by specifying the Content option. Since this is a useful thing to be able to do I thought I’d put together a detailed example of how this works.
For my example I’m going to use the Bing Maps Elevations API, which allows you to get the elevation in metres for a set of geographic locations. You can read the documentation here:
http://msdn.microsoft.com/en-us/library/jj158961.aspx
As it says at the bottom of the page, if you have a large number of locations to pass to the web service you can do so by passing them as a comma delimited list of latitudes and longitudes using a POST request. Here’s the code for a Power Query query that generates a list of latitudes and longitudes that stretches across the UK from North Wales in the west to the Wash in the east and finds the elevation for each point:
let
//Insert your Bing Maps API key here
BingMapsKey = "xxxx",
//Latitude
Latitude = 53,
//Generate a list of longitudes
Longitudes = List.Numbers(-4.5,66,0.1),
//Generate a list of latitudes and longitudes
PointList = List.Transform(Longitudes,
each Number.ToText(Latitude) & "," & Number.ToText(_)),
//Turn this list to comma delimited text
PointListText = Text.Combine(PointList,","),
//Add the text "points=" to the beginning
PostContents = "points=" & PointListText,
//Call the Elevations web service
GetElevations = Web.Contents(
"http://dev.virtualearth.net/REST/v1/Elevation/List?key=" & BingMapsKey,
[Content=Text.ToBinary(PostContents)]),
//Treat the result as a JSON document
ImportedJSON = Json.Document(GetElevations),
//Navigate to the elevations data
resourceSets = ImportedJSON[resourceSets],
resourceSets1 = resourceSets{0},
resources = resourceSets1[resources],
resources1 = resources{0},
elevations = resources1[elevations],
//Turn the elevations data into a table
TableFromList = Table.FromList(elevations, Splitter.SplitByNothing(),
null, null, ExtraValues.Error),
//Rename the column containing the elevations
RenamedColumns = Table.RenameColumns(TableFromList,{{"Column1", "Elevations"}}),
//Add a column containing the latitude
InsertedCustom = Table.AddColumn(RenamedColumns, "Latitude", each Latitude),
//Add an index column
InsertedIndex = Table.AddIndexColumn(InsertedCustom,"Index"),
//Use the index column to find the longitude for the current row
InsertedCustom1 = Table.AddColumn(InsertedIndex, "Longitude", each Longitudes{[Index]}),
//Remove the index column
RemovedColumns = Table.RemoveColumns(InsertedCustom1,{"Index"}),
//Set all columns to data type number
ChangedType = Table.TransformColumnTypes(RemovedColumns,
{{"Elevations", type number}, {"Latitude", type number},
{"Longitude", type number}})
in
ChangedType
It’s quite easy to edit the code so that it generates a list of latitudes and longitudes across the country of your choice…
Two things to point out:
- To get this to work you need to insert a Bing Maps API key in the first step where indicated. If you don’t have one, you can get your own at https://www.bingmapsportal.com
- The important step is GetElevations. The code is:
Web.Contents(
"http://dev.virtualearth.net/REST/v1/Elevation/List?key=" & BingMapsKey,[Content=Text.ToBinary(PostContents)]),
You can see here how the list of locations is passed to the Web.Contents() function (documentation here) via the Content field; notice also that I’ve had to use Text.ToBinary() on the text that I’m passing in.
Here’s the output in Power Map:
You can download the sample workbook here.
