This document discusses implementing real-time geofencing using Apache Kafka. It presents 4 approaches to join vehicle position data with geofence polygons: 1) using a cross join, 2) aggregating geofences by group, 3) using a custom UDF to aggregate geofences by geohash, and 4) aggregating geofences into a table grouped by geohash to improve performance. The document focuses on implementing these approaches using KSQL to perform stream processing on the vehicle position and geofence data streams with SQL-like queries.