Precision Object Snaps

An object snap is the cursor's ability to latch onto an exact point on something you have already drawn — the precise end of a line, the precise centre of a circle — instead of the pixel your hand happened to land on.

It sounds like a small convenience. It is not. In a program with no constraint solver, this is the mechanism that makes geometry exact. A line whose end snapped to another line's end genuinely meets it, down to the last decimal place. A line that merely looks close does not — and a trim, join, hatch or DXF export later on will notice the gap even when your eyes cannot.

Prerequisites

• You can draw a line and a circle — see Drawing Basic Shapes.

Turning it on

Snap is a button on the status bar. Click it, or press F3 (on macOS, ⌥⌘S works too). A button that is on has an outline round it.

What to expect. While a command is asking for a point, move the cursor near something already drawn. A marker appears on the exact point the cursor will catch, with its name beside it — "Endpoint", "Midpoint" and so on. Click while that marker shows, and your point lands exactly there.

The ten kinds of point you can catch

You choose which of them are active from the small arrow beside Snap on the status bar.

Three of them are off to begin with

Quadrant, Tangent and Nearest start switched off, because they fire so often that they get in the way of ordinary drawing.

Turn them on when you need them — or better, use the one-pick form described next, which is what they are really for.

Asking for one snap, for one point only

Leaving every snap running makes the cursor jumpy in a busy drawing: it keeps catching points you did not mean. The better habit is to ask for exactly one kind of snap, for exactly the next point.

How: click the input box in the context bar, type the snap's name, and press Enter. The first three letters are enough — end, mid, cen, int, per, tan, qua, nod, ins, nea.

Why you have to click the box first. While a command is running, a letter typed straight onto the drawing is read as one of that command's option keys — C means Close during Line, for example — so it never reaches the typed-input box. Only a digit, ., -, +, @ or ( opens that box on its own. A snap name begins with a letter, so it needs the click.

The other way: hold the right mouse button down on the drawing and choose Snap To from the menu that appears. (A quick right-click finishes the running command instead. How long the hold needs to be is set by Right-click hold in Preferences ▸ Cursor and Mouse.)

What to expect. A one-pick snap beats whatever else is running, applies to the next point only, then gets out of the way. You can see it has taken effect in the context bar, which changes from Next point to Perpendicular only: Next point.

This is the precise, deliberate way to work: leave Endpoint and Midpoint running all the time, and call per or tan by name on the rare occasions you want them.

How Pingendum decides which point you meant

While a command asks for a point, Snap looks at everything within a small circle around the cursor — the snap aperture, 10 pixels unless you change it — for the kinds of point you have switched on. The nearest one wins, and its marker and name appear.

When several helpers disagree, this is the order:

1. A typed point beats everything. Type 1200,400 and nothing will snap it elsewhere.
2. A snap beats Ortho's and Polar's directions, so your point lands on real geometry rather than on a tidy angle.
3. Ortho and Polar decide the direction when no snap is within reach.

Holding Shift turns Ortho off for that moment — see Drafting Aids.

Snap tracking: lining up with points you are not clicking

What it is. A way to place a point that is level with one thing and in line with another — without drawing any construction lines to measure from.

How to use it:

1. Turn on Track (F11, or ⌥⌘T on macOS) on the status bar.
2. While a command is asking for a point, rest the cursor on a snap point for a moment. A small amber + appears: the point has been acquired.
3. Move away. Dotted guides now run out from that point, horizontally and vertically, and the cursor holds to them as it crosses. Where two guides cross, your point can land exactly on the intersection.

Rest on an acquired point again to let it go. Up to seven points are held at once, until the command ends.

That is how you place something "level with that corner and in line with that centre" in a single click, with nothing to build and nothing to tidy up afterwards.

If snapping feels too eager

In Preferences ▸ Cursor and Mouse:

In a dense drawing, reduce the aperture and switch off the modes you are not using — rather than turning Snap off altogether and losing your accuracy with it.

Troubleshooting

Next Steps

Next: Drafting Aids