Not every point on a grid matters. If part of the area is water, a rival city, or simply outside where you serve, you can disable those points so the scan skips them.
How it works
On the grid, click a point to toggle it off, and click it again to turn it back on. Disabled points are left out of the scan and out of your scores, and you are not charged a credit for them.
Example: a 9x9 grid has 81 points. Disable 5 and the scan runs 76 points and costs 76 credits instead of 81.
On a scheduled geogrid, disabled points stay disabled on every run, so the credit saving repeats each cycle.
See Understanding Credits for how grid size maps to credit cost.