How to Make Maps Using Leaflet.js, PostGIS and Chicago Open Data
A fun tip, if you're using PostGIS you can actually generate the Geojson directly in the SQL query with http://www.postgis.org/docs/ST_AsGeoJSON.htmland if you're running a version of PostGIS with protobuffers enabled (Not AWS RDS) you can generate vector tiles on the fly with https://postgis.net/docs/ST_AsMVT.html
which are great for displaying large datasets.