Pre-load map tiles for smoother user experience

[jasontk19]

What existing feature could be improved?
Tiles for prev/next time step increment could be pre-loaded to improve user experience, especially when users click and hold the < or > arrows to "animate".

Describe the improvement you'd like

• Pre-cache tiles outside of animation mode
  • On page load, load tiles one step before and after current date/time
  • After a step in either direction, load tiles two steps in that direction
    • Subsequent steps will only result in loading one step worth of tiles, two steps out from current date/time
  • Pre-cache tiles when step interval changes