I am not up to speed with GMap however I offer the following information which may solve your question.
I am not associated with Laminar Research, X-Plane.Org or have any connection with the product I mention below.
Do a Google search for the follwing product called HD Mesh Scenery V3 for X-Plane 10 by alpilot. I understand the product has been developed as a replacement for the general X-plane 10 scenery. The concept is that you download the relevant file for your area, try it and then make make a financial contribution to the developer to the value you think it is worth.
Hopefully the regions (area) covered will meet your needs.
In addition have a look at the X-Plane.Org forum which discusses the product. The 196 comments can be found at http://forums.x-plane.org/index.php?/forums/topic/82197-hd-mesh-scenery-v3-for-x-plane-10-released/
Hope this helps.