The visualization does show drastic transitions but the majority of them seem to be the buses crossing the seedier areas of downtown which are, indeed, quite seedy.
You'll notice the Tenderloin (a high crime area) has its own station partitioned off from the rest of the districts. The others are also interesting. The Mission station for instance, serves a really broad community which includes both the Mission District (currently undergoing gentrification) and the Castro (gentrification complete). On the other hand, districts like Bayview, Ingleside, Taraval and Richmond are just larger, generally more residential and less in the center of everything. The Park and Northern districts on the other hand, are mostly affluent with a few outliers.
The trick with San Francisco is that because of the buckshot nature of public housing developments in the city, poor areas as mixed in surprisingly evenly with wealthy areas. This creates a lot of negative effects for residents - the expensive and trendy Hayes Valley for example, is right next door to an extremely high-crime area, the Western Addition. Keep going a bit further and you hit the Fillmore, which is again a wealthy, trendy area.
SF does this at micro-scale. In a given neighborhood there can be extremely good blocks that are directly next to extremely bad blocks. It's not hard to walk 300 feet and end up in a completely different-seeming universe.
One thing that's interesting to note is that SF buses stop very often, so the highs and lows aren't really spread across a large geographic distance, they are often separate only by a block or two. The "cliffs" in the graph really are that steep when you project it onto a map.