In the pre-10.3 world, if we wanted to show custom regions on a map we had to use custom polygons. This approach was less than optimal for a number of reasons (probably the most painful of which was changing the LOD of the viz) but one little-known one was that the polygon mark type forced server-side rendering when the workbook was published to Tableau Server. See here for the reference.

In the post-10.3 world we can now use spatial files to display custom regions which is a great big bucket of awesome sauce. However, the question came to my mind – “these are still effectively polygons, so do they trigger server-side rendering too?”

The answer, I’m pleased to report, is not necessarily.

Check out this workbook:
https://tab.databender.net/views/ShapefileRenderingTest/GCCMap?:embed=y&:jsdebug=true

This workbook shows Greater Capital City statistical areas for Australia – selected because it only has a few polygons but the source data is very detailed (~1.96M vertices). When you view the raw data from the shapefile it causes server-side rendering:

I generated (via Alteryx) some generalised versions of the same polygons – at 250m, 100m, 50m, 10m and 1m resolution:

This results in polygons with less vertices which means a simpler data set to render. The number of vertices in the data set for each resolution was:

When we select the simpler polygons for our map, we see that the rendering mode flips over to client-side rendering. Which is awesome as it gives a much smoother experience for tooltips, selections and highlighting.

In this exercise I found that when viewing all of the polygons (i.e. the whole of Australia) the cutover between client-side and server-side rendering was between 10m and 1m resolution – i.e. between 483K and 1.25M vertices. However, I also noticed that when viewing the raw shapefile resolution, if I filtered the data set to reduce the number of polygons (e.g. by selecting Victoria only – ~222K vertices) this brought me back under the threshold and allowed rendering to go back to client-side:

So the short of all of this is that working with shapefile regions works in a similar way to other dashboards when it comes to client/server-side rendering. If the complexity of the viz is over the complexity threshold then we use server-side rendering. If below, we use client-side rendering. The takeaway from this from a performance perspective is – if you are working with shapefiles and find yourself experiencing server-side rendering, consider either filtering the number of polygons or try to use a lower-resolution version of the shapefile.

As I also pointed out in my previous blog post about filled maps and low bandwidth connections, the polygon data for client-side rendering can add significantly to the size of the bootstrap package so in low bandwidth environments it might be preferable to trade responsiveness for rendering time. For the above dashboard the client-side rendering bootstrap package was 2.3M for all of Australia @ 10m resolution, vs. 5.3K for the bootstrap and 182K for the image tile when using server-side rendering.

Enjoy!