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I am unable to open your twbx file, but it sounds as though you need to either blend these files or create a join of the three in the Data Source tab. Once you have them either blended or joined, you can group them and drag to the color shelf. This link may help. http://kb.tableau.com/articles/howto/decding-between-joining-tables-and-blending-data
Thanks so much for your help. I managed to figure it out after a bit more tinkering. I apologize if I wasted your time, and I really appreciate your effort.
- What I did was I combined all of the LAT/LONG coordinates into a single Excel sheet as a single data source. I also added a new column called Type, which indicates what kind of coordinate the data point represents. Let's call these Types A, B, C, and D.
- Then, I created the point distribution map by dragging LONG onto Columns and LAT onto rows, changed the pills from AVG to Dimension, which automatically generates the point distribution map. At this juncture, I have 4 types of data points but Tableau just interprets all of them as coordinates, so they are all colored the same teal-grey/bluish color (I actually have 4 sets of data not 3 as in my original question).
- I then looked at the Dimensions on the left hand panel, and dragged Type (the newly created column) onto the Marks panel, which automatically generated a color palette and automatically selected a color for my data points corresponding to what Type it was. I could then edit the colors/palette as I wanted.
This third step is the trick; for some reason it was not intuitive to me. However, after reading lots of other community posts in trying to solve this issue, I realized a lot of the interface relies on things that you drag and drop. So I just thought "Type" is something I want to use to dictate the display of the Marks, so that's what I did.
Thank you again for your help!