Category: map

Using PowerBI M Parameter to calculate a polygon Area

TL;DR : PowerBI does not support GIS Area calculation, in this blog we use M Parameter to leverage third party Database to do the calculation, Works only In Direct Query Mode.

ink to Public report

With the Update of August 2021, M Parameter support multi value selection, see this Previous blog for a little background, this open some interesting new use cases that was not possible before in PowerBI.

Again, before you get too excited, it works only with Direct Query and Database that support M Parameter ( BigQuery, Snowflake, Azure ADX etc)

One example is calculating the area of a group of arbitrary points

  • In Icon Map, I select a group of points (Notice here, Icon map is acting as Parameter Action filter )
  • The List of points are used in an M Parameter
  • A SQL Query is sent back to the Database that support M Parameter in my case I am using BigQuery
  • BigQuery generate a wkt and calculate the area , you can calculate the distance too or any metrics that use geometry
  • Plot the results in another Icon Map

The Query is straightforward, and the best part because we are not running a Query against any table in BigQuery , it does not cost anything, you can register here for free and no credit card is required

Here is the M Query

let
TagsList = 
    if 
    //check to see if the parameter is a list
      Type.Is(
        Value.Type(tag_selection), 
        List.Type
      ) then 
        //if it is a list
        let
          //add single quotes around each value in the list
          AddSingleQuotes = List.Transform(
              tag_selection, 
              each "'" & _ & "'"
            ),
          //then turn it into a comma-delimited list
          DelimitedList = "[" & Text.Combine(
              AddSingleQuotes, 
              ","
            ) &"]"
          
        in
          DelimitedList
    else 
      //if the parameter isn't a list
      //just add single quotes around the parameter value
      "['" & tag_selection & "']",
      
Source = Value.NativeQuery(GoogleBigQuery.Database([BillingProject="xxxxxx"]){[Name="xxxxx"]}[Data], "WITH
  xxx AS (
  SELECT
    *
  FROM
    UNNEST( "& TagsList &" ) AS element),
  yyy AS (
  SELECT
    ST_CONVEXHULL( ST_UNION_AGG(ST_GEOGFROMTEXT(element))) AS geo
  FROM
    xxx)
SELECT
  ST_ASTEXT(geo) AS WKT,
  st_area(geo) AS area
FROM
  yyy", null, [EnableFolding=true])
in
    Source

And here is the result.

Future Improvement

One thing I would really like is the possibility to show the result in the same Map, unfortunately to the best of my knowledge a Table in DAX can not filter itself, see this example

Image

in Icon map it is possible to display wkt and points at the same time , but as you can see from the screenshot wkt geometry in the table does not change based on internal filter selection, the other viz works fine.

M Parameters has a very interesting application, and I am excited to try other tricks 🙂

Edit : I appreciate some votes here for the option to pass filter selection to the same Visual

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Dynamic Geospatial Clustering using BigQuery GIS

I was reading this blog post and thought of a new use case, using OpenstreetMap Data and generate polygons based on the user Selection

First to reduce cost, we will select only all a subset of OpenstreetMap Data, you can use this post as a reference

my base table is OPENSTREETMAPAUSTRALIAPOINTS , which contains 614,111 rows

The idea is to provide some tag selection ( School, cafe etc) and let BigQuery generate a new polygons on the fly, the key function in this SQL script is ST_CLUSTERDBSCAN

WITH
  z AS (
  SELECT
    *
  FROM
    `test-187010.GIS.OPENSTREETMAPAUSTRALIAPOINTS`
  WHERE
    value IN UNNEST(@tags_selection)),
  points AS (
  SELECT
    st_geogpoint(x,
      y) AS geo_point,
    value AS type
  FROM
    z ),
  points_clustered AS (
  SELECT
    geo_point,
    type,
    st_clusterdbscan(geo_point,
      200,
      @ct) OVER() AS cluster_num
  FROM
    points),
  selection AS (
  SELECT
    cluster_num AS spot,
    COUNT(DISTINCT(type))
  FROM
    points_clustered
  WHERE
    cluster_num IS NOT NULL
  GROUP BY
    1
  HAVING
    COUNT(DISTINCT(type))>=@ct
  ORDER BY
    cluster_num)
SELECT
  spot AS Cluster,
  st_convexhull(st_union_agg(geo_point)) as geo_point,
  "Cluster" as type
FROM
  selection
LEFT JOIN
  points_clustered
ON
  selection.spot=points_clustered.cluster_num
  group by 1
union all
SELECT
  spot AS Cluster,
  geo_point ,
type
FROM
  selection
LEFT JOIN
  points_clustered
ON
  selection.spot=points_clustered.cluster_num

Technically you can hardcode the values for Tags, but the whole point is to have a dynamic selection

I am using Data Studio and because the Query is not accelerated by BI Engine , and in order to reduce the cost, I made only 6 Tags available for user selection and hard code the distance between two points to 200 m.

Here is an example when selecting the tags (restaurant, school and fuel), I get 136 cluster

here when I zoom on 1 location, the result are pretty accurate

I think it is a good use case for parameters, GIS calculation are extremely heavy and sometimes all you need from a BI tool is to send Parameter values to a Database and get back the result.

you can play with the report here

edit : August 2021, The Same report using PowerBI

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