Grid lines mark off 10-year periods, but the superimposed dates and images appropriately reflect fuzziness and scholarly disagreements.

There are only grid lines on this map.

Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to features.

The same diagram may show the angle of grid north (the direction of the map's north-south grid lines), which may differ from true north.

Pieces always sit on the points of intersection of the board's grid lines.