The grid spacing is the distance in map units separating grid lines. Increasing the grid spacing decreases the grid density.
With Auto On enabled, increasing the grid spacing results in a decrease in the grid lines in order to the relationship: [lines-1]*[spacing] = grid length.
With Auto On disabled, grid spacing can be changed independently of the grid lines. If you only change the grid spacing, an error message will appear, warning you that you must also change the grid lines and/or grid length to maintain the relationship: [lines-1]*[spacing] = grid length.
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