2 Replies Latest reply on Aug 17, 2018 2:38 PM by Sarah Battersby

    Using Albers Equal Area projection as background image

    Ben Paulos

      I am trying to make a map with a background image that is a US map of wind speeds made in an Albers Equal Area projection (WGS84). 

       

      But Tableau uses Web Mercator, so my data marks are not in the right lat/long positions.

       

      I have about 1000 data points so I don't want to place them all individually, which is one option (see here).

       

      I read Sarah Battersby's blog on this topic, but I am not able to recreate the image with GIS data.  I have to use an existing image file.

       

      Is this possible in Tableau, or should I use QGIS or some other program?

       

      - Ben Paulos

        • 1. Re: Using Albers Equal Area projection as background image
          Patrick A Van Der Hyde

          Hello Ben,

           

          Were you able to locate a solution for this project?  I notice how much this looks like a heat map as well and want you to be aware that heatmaps are a coming very soon - Coming Soon: New features in Tableau  and you may be interested in trying the current beta to determine if this would work for this situation.

           

          Patrick

          • 2. Re: Using Albers Equal Area projection as background image
            Sarah Battersby

            Hi Ben,

             

            If I'm understanding the problem correctly, I have an idea on how to do this... I made a quick example and attached (wind speed map as an image and US state capitals as a point dataset on top).

             

            To make this, I did some outside processing in QGIS:

            • Georeferenced the wind speed GIF to obtain the left/right/top/bottom coordinates for the black outline.  I used a Census boundary shapefile of states for my reference points and just picked a handful of distinct locations (e.g., the tip of the Olympic peninsula in WA state, the southernmost point in TX, etc.). Before georeferencing, I reprojected the US boundaries to Albers equal area.  The result of this is a geotiff.
            • Added the georeferenced file to QGIS and grabbed the bounding coordinates from properties

            • Added a shapefile with coordinates in lat/lon to QGIS.  Reprojected to Albers equal area.
            • Added an X and Y column for the shapefile so that I had columns with the x,y locations in the projected Albers equal area projection

             

            In Tableau:

            • Add my shapefile (or a CSV...you aren't going to use the geometry from the shapefile, so the format doesn't matter...you just need the new x,y columns with the projected coordinates)
            • Add the geotif to Tableau as a background image.
            • Set the left/right/top/bottom coordinates based on the geotiff bounding box identified in QGIS.
            • Drop the x,y coordinates on the viz.

             

            If I've understood your problem correctly, I think you should be able to automate translating your points into a viz this way...

             

            -Sarah
            Tableau Research.

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