A map of every highrise (above 35m in height) in Austin:
http://skyscraperpage.com/cities/maps/?cityID=93
There's a very clear triangle of density between the points I mentioned, with only scattered highrises outside of that triangle. In fact, you might even go so far as to say that there's a square. Austin's density, in the current built form, is not just along the river and not even just primarily along the river. And it is getting less so.
Put your money where your mouth is.