I think nom-nom is trying to imply that if you're passing GBs of Json around, "human readability" isn't probably a concern. Therefore you could go for an efficient binary format.
JSON isn't just about human readability, it's about being a 'good enough' standard for data exchange. What binary format would you use that people could parse as reliably as JSON?
In case your question wasn't rhetorical, I believe MessagePack is the leading schema-less binary serialization format (which does not contradict your point as it is still less ubiquitous than JSON).
Maps. [0] Geo-cordinate data can consist of tens of thousands of data points. For example, think of a two dimensional space with a co-ordinate grid at regular intervals representing a 20km x 20km city. Then imagine creating an outline of a city road network. Each point a LAT/LON co-ordinate. Then imagine placing thematic data such as known traffic hot spots.