Shelyn comes to mind immediately. Cartography is definitely an art, and I can see many cartographers following her. Her cartographers would focus on details and making the maps pleasing to the eye.
Abadar is also a good choice. His cartographers would likely focus on economic points of interest, and have very utilitarian maps.
The Empyreal Lord Keltheald would have cartographers who create maps that would focus on natural landmarks, particularly those with amazing views for admiring natural beauty.
I can see both Cayden Cailean and Erastil having cartographers in their followers who create land use, farming, and crop maps, as their areas of concern both have agricultural interests (the agri-supply side of alcohol for Cayden, community farming for Erastil).
There is also an ancient Azlanti deity Elion whose areas of concern are exploration, discovery and colonization. Map makers, particularly those concerned with ancient maps, may find this a good deity.
Maybe why they are cartographers would shed light on which deity to worship.
A Military Cartographer might go with Gorum, Iomedae, or Asmodeus
Love of travel and adventure? Desna or Cayden
The art of the map? Shelyn
Bringing civilization to wild places? Erastil, Abadar, or Asmodeus
Establish trade route? Abadar
Document for history? Irori