2. You can use BufferWithTolerance() to create a simple approximation of a circular polygon containing less sides. With an appropriate tolerance, you might be able to create a hexagon, but you can't specify the number of sides and it would be slightly trial-and-error.
If you really need to create specific geometric shapes you're best off creating a custom SQLCLR method to do so.

but this is geometry and cartesian coordinates. Although I can easly convert it into geogprahy, this still will not be a x kilometer radius. Some proportion could be used as a relation of degrees to km, but 1 km expressed as degrees differs on each
point on earth (GPS - 4326).

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