Map marker clusters and more user-friendly UI changes!

A big big thank you to open source developer Leigh Halladay, who published this useSupercluster hook for React:

use-supercluster npm package

use-supercluster Github page

I had been wanting to do map marker clustering using Mapbox and React, but hadn't found a solution until I stumbled on Leigh's library, described here.

This finally allowed me to cluster markers together, allowing me to publish sportsmap.world with a much friendlier interface for mobile users.  I've made additional changes to make the site more smartphone and mobile friendly, as that's the primary experience for most people browsing the web these days!

More UI upgrades since November:

- A better mobile calendar experience, including a dropdown calendar widget to allow you to select a date range, rather than relying on the double-date slider (which is still present for wider screen).

- A filter-by-sport widget, to remove specific sport pins from the map.

- Fast load times & optimized queries, plus a loading spinner while the initial query is in progress