From #openttdcoop wiki
Altering the world around you
Part 1: Removing a city
Sometimes cities get in the way of building a mainline or something else. Here's how to get rid of it.
Part 2: Dodging unremovables
Often times antennaes on top of mountains, lighthouses on the shore, or just an industry in the wrong spot get in the way. The ways to get around this are explained here.
Part 3: Terraforming
Sometimes we have to shape the terrain in order to make room for stations or hubs. This article explains when to terraform and how much.