Snapping

How the cursor finds the point you meant.

Move the cursor near something and a small diamond appears, with a word for it in the bar along the bottom. That diamond is where the next click will land - not where the pointer is.

The cursor walks along one edge and the diamond changes color and name at a corner, at a crossing, along the edge and at its midpoint. — The cursor walking along a single edge, touching nothing else. The diamond changes color and the bar renames it at every stop - the end of the edge, where something crosses it, the plain middle of it. Nothing was clicked in that whole sequence.

What it finds, and the color it uses

Color	What
Green	ENDPOINT	a corner, or the end of a line
Green	CENTER	the middle of a circle or an arc
Cyan	MIDPOINT	the middle of a whole edge
Cyan, hollow	ON SEGMENT	the middle of one piece of an edge that something crosses
Red	ON EDGE	anywhere along an edge
Violet	CROSSING	where two edges - or two guides - cross
Blue	ON FACE	on the surface, when nothing better is near
Yellow	ORIGIN	0,0,0
Axis color	ON RED / GREEN / BLUE AXIS	on one of the three lines through the origin
Magenta	PARALLEL TO EDGE	along the edge the line started on, or the piece just drawn
Magenta	PERPENDICULAR TO EDGE	square to that same edge, in the plane you are drawing on
Accent	GRID	the SNAP TO step, when there is nothing else - a dot, not a diamond

A corner beats a midpoint, a midpoint beats a point on an edge, and anything beats the grid. That order is why you can aim roughly at a corner and still get the corner.

Reading it before you click

The word in the bar is worth trusting more than your aim. If it says ON EDGE when you wanted ENDPOINT, move a few pixels rather than clicking and undoing.

When the cursor is lined up with something - an axis, a point it is level with, an edge it runs parallel or square to - a heavy dotted line runs from that thing to the cursor in the color that says which. The card beside the cursor moves to the side the line is not on, so the line you are following stays in sight.

Holding a direction

The arrow keys lock an axis: right locks red, left locks green, up locks blue. Down lets go. The rubber band turns that color to say so.
Shift, during a move or a drag, keeps whichever axis it has already drifted onto.
Type a length and press Enter and the direction is whatever is locked or inferred, at exactly that distance.
Alt, part way along a line, steps through what may be inferred: all of it, then the directions off, then parallel and square to the last edge only. This is SketchUp's cycle, on SketchUp's key. Points - corners, midpoints, crossings - keep snapping whichever stop you are on.

The grid step

SNAP TO, on the SETTINGS menu, is how far apart the grid points are - 1/16", an inch, a foot. It is the fallback when nothing else is near, so it never gets in the way of a corner. Set it to what you are working to and rough clicks land on round numbers.

When nothing is near enough

Zoom in. The reach is in pixels, so zooming makes it choosier without changing any setting. This is also the fix when two things are close together and it keeps taking the wrong one.

What it finds, and the color it uses

Reading it before you click

Holding a direction

The grid step

When nothing is near enough

See also