4 Replies Latest reply on Apr 5, 2013 12:57 PM by Chris Foster

    Dual Axis: correctly pairing Longitudes and Latitudes?

    Chris Foster

      Hi -

       

      I'm trying to use Dual Axis view to map two pairs of longitude and latitude coordinates onto the same background image, and I can't figure out a way to ensure that data is only plotted for the correct pairings of longitude and latitude. Is there a technique or trick that I've missed?

       

      (WARNING: I'm new to Tableau, and may be tripping over fairly obvious-in-hindsight newbie problems.)

       

      The goal is to plot two X/Y positions over time, using the Pages card to visualize their motion as a timestamp increments.

       

      Each record of my database contains these fields (among others):

       

      • alpha_X (dimension, latitude, continuous)
      • alpha_Y (dimension, longitude, continuous)
      • beta_X (dimension, latitude, continuous)
      • beta_Y (dimension, longitude, continuous)
      • time_index (dimension, discrete)

       

      My goal is to have this result in two coordinates, (alpha_X,alpha_Y) and (beta_X,beta_Y), animating across the map using time_index in the Pages card to drive the animation.

       

      Here's what I've set up:

      • I'm using a custom background image, with appropriate coordinate scaling
      • both X's and used as columns
      • both Y's are used as rows.
      • Both X's and Y's are set to be Dual Axis
      • Each X was set with a different Mark Type to allow them to be given different shapes, colors etc.
      • time_index was dragged into Pages.

       

      The result of this is that I have FOUR marks:

       

      • (alpha_X,alpha_Y), mark type Alpha = CORRECT
      • (beta_X,beta_Y), mark type Beta = CORRECT
      • (alpha_X,beta_Y), mark type Alpha = INCORRECT
      • (beta_X,alpha_Y), mark type Beta = INCORRECT

       

      So it appears that it's plotting both Y values for each X value. Which leads to a bunch of questions:

       

      • Is there something I can do -- maybe via Level of Detail -- to cause Tableau to exclude the errant coordinate pairs?
      • Would it change or simplify things if the two coordinates were blended in from different databases?
      • Is there a smarter way to achieve this setup?
      • Does Tableau not support this use of the dual axis feature?

       

      Thanks for any help you can provide. If I've left out relevant details about my setup, feel free to ask questions and I'll clarify.

       

      -- ChrisF