City of Titans haven't been shy about praising the Unreal Engine 4 at the heart of development. A new design article gives some insight into one of the major elements of design that makes it so useful to the team, a feature that offers rapid progress between brainstorming, prototyping, and testing: blueprints.
While the article doesn't contain the nuts-and-bolts of the programming elements, it demonstrates how the team was able to build and test a tile-based map system (akin to Skyrim) as an independent element to be tested. The result is that instead of spending a great deal of time brainstorming the idea, the team can drop the prototype in for testing and it can be evaluated as an actual option instead of simply a theory. Take a look at the full article for more details on the map system and the test process.
[Thanks to Byron for the tip!]