I had a city with 25000 citizens, but it started to decline. As you can see on the screenshot there are a lot of empty spaces. There used to be building along those roads. 

[![Shrunken OpenTTD city][1]][1]

[![City center with abandoned spots][2]][2]

To prevent the decline I added bus routes within the city. According to the OpenTTD wiki that's a way to increase town sizes:
> A bus with one passenger from the other side of town would have the same effect on growth as a large train full of passengers from the other end of the map. source: [wiki.openttd.org](https://wiki.openttd.org/Town#Tips_for_Town_Growth)

But the city still shrinks. Does somebody know how to prevent this?


  [1]: https://i.sstatic.net/T2nGR.jpg
  [2]: https://i.sstatic.net/b6sp2.png