Preferences > Grid

Settings of the grid that can be drawn over the map view. The grid is a visual aid for laying out and checking mapping, for example to see which districts of a city have been edited or to plan a regular street pattern. It is drawn above all layers and there is no snapping to it: drawing and editing are not affected by the grid.

The grid is switched on and off with View > Grid > Show; the checkbox at the top of this tab does the same. This tab can also be opened directly with View > Grid > Grid preferences....

Grid type

Projected coordinates

Straight lines of constant east and north coordinate of the current map projection. This grid can be rotated and has a spacing given in metres. This is the default and the right choice for regular street patterns or a "one kilometre" work grid.

Latitude/longitude

Lines of constant latitude (parallels) and constant longitude (meridians) with a spacing in degrees. In most projections these lines are curves; they are drawn accordingly. The grid cannot be rotated.

Spacing

East spacing / Longitude spacing

Distance between the lines running north-south, i.e. between neighbouring east coordinates or meridians.

North spacing / Latitude spacing

Distance between the lines running east-west, i.e. between neighbouring north coordinates or parallels.

For a projected grid the spacing is a true distance in metres, as measured by the parallel way tool and shown in the status bar, and not in raw projection units (in the default Mercator projection those are metres only at the equator). The conversion is done at the grid origin, so the grid is exact there and drifts very slightly with distance from the origin (about 0.3 % per 50 km north or south at 20° latitude). Place the origin in the area you work in, see below.

For a latitude/longitude grid the spacing is in degrees; decimal values like 0.25 are allowed.

Rotation (degrees)

Rotation of a projected grid around its origin, counter clockwise, in degrees. Since a rectangular grid repeats every 90°, a rotation of 64° is the same grid as −26°. The rotation is ignored for a latitude/longitude grid.

The rotation can also be taken from existing data: select a straight way (or exactly two nodes) that runs along the desired grid direction, then View > Grid > Align rotation to selection, see Map view > Grid.

Origin

Origin east / Origin longitude

East coordinate resp. longitude of a point through which a north-south grid line passes.

Origin north / Origin latitude

North coordinate resp. latitude of a point through which an east-west grid line passes.

The origin fixes the position of the grid lines. The easiest way to set it is to select the point where two grid lines should cross (for example the node at a street intersection) and choose View > Grid > Set origin to selection; this fills in both values and switches the grid on. If more than one node is selected (or a whole way, or a relation), the centroid — the arithmetic mean position of every node reachable from the selection — is used instead, so any selection works, not only a single node. For a projected grid the origin is also the point where the metric spacing is exact.

Minimum line distance on screen (pixels)

When zooming out, the lines of the configured grid would get closer and closer together. Below this distance (in pixels) the spacing is multiplied by 10, and by 100, 1000, ... if needed, until the lines are far enough apart. The coarser grid is always aligned to the configured one, so a 1 km grid becomes a 10 km grid whose lines are also lines of the 1 km grid. The default is 25 pixels.

Line width (pixels)

Width of the grid lines. The default is 2.

Blend mode

How the lines are combined with the map below them:

Normal

Ordinary transparency, the line color is painted over the map.

Multiply

Darkens the map by the line color; white is neutral.

Burn

Darkens strongly and increases the contrast; white is neutral.

Hard light

Line colors darker than mid grey darken the map (like multiply), lighter colors brighten it (like screen). A bright color such as yellow stays visible over both light and dark map features. This is the default.

Difference

Absolute difference between line color and map; a colored line is visible on any background, black is invisible.

Divide

Brightens the map; dark line colors give bright lines, white is neutral.

Colors

The colors of the two line directions are set in the Colors tab:

grid east lines

Lines of constant east coordinate resp. meridians (the lines running north-south).

grid north lines

Lines of constant north coordinate resp. parallels (the lines running east-west).

Both default to yellow (#FFFF00). Using two different colors makes it easier to tell the directions apart on a rotated grid.

Preference keys

Key	Default	Meaning
draw.grid.enabled	false	grid shown
draw.grid.type	PROJECTED	PROJECTED or LATLON
draw.grid.spacing-x	1000	east resp. longitude spacing
draw.grid.spacing-y	1000	north resp. latitude spacing
draw.grid.rotation	0	rotation in degrees
draw.grid.origin-x	0	origin east resp. longitude
draw.grid.origin-y	0	origin north resp. latitude
draw.grid.min-pixel-spacing	25	minimum line distance on screen
draw.grid.line-width	2	line width in pixels
draw.grid.blend-mode	HARD_LIGHT	NORMAL, MULTIPLY, BURN, HARD_LIGHT, DIFFERENCE or DIVIDE
color.grid east lines, color.grid north lines	#FFFF00	line colors

See also

• Map view > Grid: showing the grid, setting origin and rotation from the current selection
• Parallel way tool: offsets in true metres, matching the grid spacing
• Map Projection

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