It is advisable to decide what will define the extent of the vector grid before you start
the tool. This can either be a feature or raster layer, or a set of coordinates that you
manually type in. Note that for reference layers, the extent is considered to be the
rectangle that bounds the layer.
Lines or polygons as output?
For map production purposes, using lines as the ouput feature is likely to be the most useful
because a LABEL field is added to the attribute table and coded with the appropriate
coordinate for graticule labeling (the X coordinate for vertical lines, and the Y coordinate
for horizontal lines). For tiling datasets or for spatial analysis purposes, the polygon
output is likely to be most apprpriate.
How does the snapping work?
If you opt to snap the grid to major coordinate system intervals, the tool will use the
interval you specify to determine where the snap should occur. For instance, if you use an
interval of 1000m, the grid will be snapped to the 1000m mark of the UTM grid. If you use an
interval of 10m the grid will be snapped to the 10m marks of the UTM grid. For uneven intervals
like 2045.67, the tool will look at the number of significant digits (SD) before the decimal
place (in my example 4), and snap the grid to the first major interval defined by:
1 x 10 ^ (SD-1)
which in my example is 1000.