The markers are the lighthouses on the upper edges.
Have also marked the center.
There are no objects yet, just green terrain that is absolute flat.
See the screenshots and scn-files.
If some of you have a easier way to do a "measure and marking" it in a scenario,
I am interessed to hear about it.
The scenarios are given away as public domain.
Use them to create your own "industry/city rich" scenarios.

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This scenario attached:
Scenario size is 512x512 and it in the temperate climate.