1 Reply Latest reply on Sep 20, 2016 6:47 PM by Kathryn Bridges

    Create filled map with two data sources without field to join on

    Amanda Lamb

      Very new user here, so please forgive what is probably a very basic question and if I phrase things incorrectly. I am trying to build a map of 911 call volume by neighborhood. I have a dataset with the individual calls-for-service incidents (with details like nature of call - robbery, traffic accident, etc.) joined to another file with the latitude and longitude of each incident. I can create a map using this joined data with dots for all the incidents. The resulting map looks like this:

       

       

      I would like to create a fillable map using polygons derived from neighborhood boundaries. I have that file with neighorhood boundaries formatted for Tableau. The resulting map looks like this:

       

       

      I would like to combine these two datasets to create a map of call volume by neighborhood. I think the problem is that there is no field to join the data on. I don't have any incident information (or even city, state, etc.) in the neighborhood boundaries map. The result would look something like this (this is a Seattle example with the higher number of incidents shaded darker red):

       

       

      So how do I either 1.) bring in two datasets that aren't connected and build a map using data from both, 2.) join the data together somehow even though there are no common fields, 3.) create a fillable map some other way I don't know about, or 4.) conclude that it can't be done (I think that is unlikely).  I think since I'm so new I don't even know how to phrase my question to get an answer through these forums. Any advice or links to other forum topics would be very helpful, thank you!

        • 1. Re: Create filled map with two data sources without field to join on
          Kathryn Bridges

          Hi Amanda,

           

          I think I understand what you're asking, but I also may not explain it the best. It sounds like at the end of the day, you have latitude and longitude in both of your datasets, yes?

           

          Dataset 1- 911 calls & location

          Dataset 2- Neighborhood boundaries (polygons)

           

          Just to get the map, you'll want to "union" the data, so that the Latitude and Longitude fields of both of these data sources are in the same column, and then all the other columns are there. You'll have some blank fields, but don't worry- "Call type" will be null in all the rows with the neighborhood data, and "Polygon order" will be blank in all the rows with 911 location. If you create the sheets with all the columns needed in both, you can union them in Tableau, but your life will probably much easier if you can do it in a statistical program like R.

           

          The issue is that even though the map will look correct, you still won't be able to filter the calls based on neighborhood, since you won't know what neighborhood the calls are in. What I would suggest it using another data source (Census data? Do you know what City the calls were from and what cities are in what neighborhoods?) to assign the calls to a zip, city, or neighborhood, so that you can have another column that the two data sources will also share.

           

          Hope this helps! Maps are one of the most fun parts about Tableau (=

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