Shading within a single layer

Hi all,

I am attempting to make a map of an area for a gift.  I stitched together 60 tiles from google earth.  On photoshop you can clearly see the differences in the shading/color that appear in straight vertical lines (see attached).  These appear to be shading differences within the same screenshot/layer on google earth.  Does anyone have any advice on how to best blend this together so that it looks more uniform?

Thank you