Software design is usually discussed as if the system is being created “de novo”, but most programmers are working on systems that have already been released. This is a sign of success, since software is now good enough to keep and is worth improving. But the way we talk about design and the way we teach it is stuck in the twentieth century. The software frontier is closing. Although there are still new projects, it is more accurate to say “there are no new software projects” than it is to say “all software projects are new”. What would the world be like if there were no new software projects? If a software project has been going for fifty years then a programmer who has been on the project for twenty years will be more valuable than someone who is new to the project. Old programmers will be more valuable than young programmers. If a software project is going to last another fifty years and will be actively developed during that time then it is worthwhile to keep it in good shape. It is worth fixing pesky bugs that only appear once every year. It is worth spending some time improving the documentation. It is worth rewriting parts of the system that are complex and buggy. If a software project is on version 129 then it is clear that software development is program transformation. Each iteration transforms version N into version N+1. Although user requirements are important, version N+1 depends more on version N than it does on the latest requests from the users. Fortunes can be made both on the frontier and in cities. The frontier and cities are different, however, and some of the rules of success of the frontier must change for the cities.