Update README.md

README.md

@@ -1,10 +1,15 @@
 # Beacon map
 This map shows all the blinking beacons from [OpenStreetMap](http://www.openstreetmap.org/).
 
-More specifically, it asks the [Overpass API](https://www.overpass-api.de) for all elements with an `seamark:light:sequence` attribute, decodes these, and displays them as coloured circles on the map. It also tries to take the `seamark:light:range` and `seamark:light:colour` into account.
+More specifically, it asks the [Overpass API](https://www.overpass-api.de) for all elements with an `seamark:light:sequence` attribute, decodes these, and displays them as coloured circles on the map using [Leaflet](http://leafletjs.com). It also tries to take the `seamark:light:range` and `seamark:light:colour` into account.
 
 ## Overpass API
 The current version uses an extracted dataset, but the code allows for directly querying the Overpass API. However, since a query like the one used here can take multiple minutes to complete it is not very useful do always do live queries.
 
+## Useful stuff
+The `leaflet.indexedfeaturelayer.js` file contains an extension on Leaflet's GeoJSON layer that only add layers/features to the map that are (or are about to be) visible. It uses a spatial index to quickly query which features can be removed from the DOM, increasing performance.
+
+`leaflet.light.js` contains my best guess on how a light sequence will look based on (these descriptions)[http://wiki.openstreetmap.org/wiki/Seamarks/Light_Characters]. However, it might be inaccurate, and it tries to do its best with the sometimes not entirely consistent data from OSM.
+
 ## Credits
 This map is made by the [Geodienst](http://www.geodienst.xyz) because it was a fun idea we wanted to try out. Feel free to fork this map and make your own visualisation of OSM data, or contribute improvements back to us.