Photoshop being an image editor has limitations on the pixel resolution at file setup. If you set for high resolution and many inches in scale, it can look good, but ideally once you set your resolution parameters, the resolution is fixed and cannot be easily altered in size. While maps created in vector programs like Illustrator can easily rescale, only those maps entirely created in vector and safely rescale without an problems. If you import a map created in an image editor and import to a vector program it still has fixed pixel resolution, so cannot effective rescale. When I create maps in vector applications like Xara Photo & Graphic Designer I don't even worry about pixel resolution until I am done with the map and at the image export stage, then I scale it in inches to my desired scale, then export at whatever resolution is needed with 100 ppi for Virtual Tabletop apps, or 300 ppi for print. Such features are only available using vector drawing applications.
Essentially, no, you cannot effectively rescale an image created in Photoshop with best results - image will blur and lose color fidelity if you try to scale it larger.