How to create an evacuation routes overlay

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By combining the output of the Water Overlay's results on water heights, and the Travel Distance Overlay, it is possible to create a calculation model for valid evacuation routes in the event of a water calamity.

How to create an Overlay for calculated evacuation routes:
  1. Add a Rainfall Overlay.
  2. Set the amount of rainfall of the Rainfall Overlay to a total of 60mm in 60 minutes, followed by 0 minutes of dry period.
  3. Add a Combo Overlay, with the Rainfall Overlay set to input A, and a formula of "GT(AT, 0.2)". This computes all places where a route would be blocked (1) or not (0), by having more than 20cm of water stress.
  4. Add an Area, and draw it anywhere in the project area and with an Attribute named DESTINATION_AREA set to 1. This location will be the evacuation point.
  5. Add a Travel Distance Overlay.
  6. Under "Keys", opt to use a "blocking input", and select the Combo Overlay created earlier. This will disqualify certain routes from being traversed.
  7. Recalculate, and play the Travel Distance Overlay
  8. Notice that as the simulation progresses, the green evacuation routes will be supplanted with red indications that the road is experiencing too much water stress.


  • The setup could be further expanded on by adding an additional Combo Overlay which takes into account which locations were once a valid route but later weren't, thus highlighting all the locations which become cut off from evacuation routes.

See also