The document discusses building a real-time heatmap service using Apache Storm.
[1] It proposes using a Storm topology to process streaming check-in data in real-time, geocode the locations, build heatmaps for time intervals, and persist the results.
[2] The topology would include spouts to generate simulated check-in data and read from Kafka, bolts for geocoding, building heatmaps, and persisting to a database, and would scale horizontally by increasing parallelism.
[3] The document outlines the components, provides code examples for the spouts and bolts, and discusses options for integrating a messaging system like Kafka to make the topology more robust and scalable.