Yes, the sandbox maps all start the same. How ever, you can go into the Steam workshop and download maps that have been terraformed by other people and build your park on that.
The same is true of the Challenge parks (and if you say its not, you haven't been looking in the workshop properly, there are at least 10 pre-terraformed parks for the Challenge mode, I know.. I made them.)
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We could use a scenario editor. Preferably one that can import height-maps. But, I can wait... No rush.
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PC Does actually use a 'sort' of square mesh terrain system. It doesn't have the grid lines because that would be too constraining for the freeform style they are going for. The terrain tools are designed to soften out hard edges, but if you are smart you can work around that. That said, I think an option to turn on the Grid/vertex geometry of the terrain would be nice for those people who need a little less freedom.
If you missed the Mesh lines.. They are easy to see of you point the Camera directly South, youll see the repeating pattern of the terrain texture. Once you see it, youll be able to get away from that nasty freeform smooth edged feel and go back to working in a predefined constraining Grid system. The tools are there, you just have to use them.
Terrain high can be a problem to start with. But again, there are ways around that.
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This isn't RCT3.5 This isn't RCT4 (for good reason).. This is Planet Coaster. This is v1.1.2 and this is still inside its first 90 days.