You drag a box around some wall lines, type erase, and find half of them still there. Or the opposite: a small box goes round and the whole drawing disappears. Both come from the same thing, and that thing is which way you dragged.
Selecting objects in AutoCAD offers two box types that look almost alike and behave nothing alike. This article measures both over the same set of geometry, then works through the reasons a line sitting in plain view refuses to be picked at all. For the full set of drawing skills see our AutoCAD for Construction course.
A window selection and a crossing selection are not the same box
Drag left to right and you get a window: blue fill, solid border. It takes only objects lying entirely inside.
Drag right to left and you get a crossing: green fill, dashed border. It takes anything the box merely touches.
Six real lines show the gap. Three short ones run from 1500 to 3500, three long ones from 500 to 6000. One selection box, from 1000 to 4000 horizontally: it encloses the three short lines completely and merely cuts across the three long ones.
| How the box was dragged | Caught |
|---|---|
| Window, left to right | 3 lines |
| Crossing, right to left | 6 lines |
| The whole drawing, for comparison | 6 lines |
The third row is there to show the drawing holds six lines in total. So the window misses exactly half, while the crossing takes everything.
Neither is more correct than the other. Erasing a whole cluster calls for a crossing. Picking a few items inside a region without disturbing the lines running through it calls for a window.
Why a box comes up short
Nearly every case of a selection box missing things is one of these four.
Dragged the wrong way. The commonest by far. To catch everything, drag right to left. The fill colour says which you have: blue is a window, green is a crossing.
Let go of the button too early. The PICKDRAG variable governs how the box is drawn. On the 2027 release it reads 2, meaning both routes work: click, release, click again for the second corner, or hold the button down and drag in one motion.
Started on an object instead of empty space. The first corner has to land on empty space. Landing on a line selects that line instead. PICKBOX reads 3, the radius in pixels of the pick aperture around the cursor — the bigger it is, the easier it is to catch something by accident.
The objects are off screen. A box only catches what is currently displayed. Zoom out until everything shows, then drag again; zooming is covered in our article on the zoom command in AutoCAD.
When an object refuses to be picked at all
When a line is plainly on screen and clicking does nothing, work down this list.
Its layer is locked. This is cause number one. Autodesk's layer locking page puts it in one line: "You cannot edit the objects on a locked layer; however, they are still visible if the layer is on and thawed". The giveaway is clear enough: objects on a locked layer are faded, and hovering over one shows a small padlock. How faded is set by LAYLOCKFADECTL, which reads 50 on the 2027 release.
Unlock with LAYULK, or click the padlock in the layer palette. Layers are covered in our article on layers in AutoCAD.
It is inside a block. Clicking one line of a block selects the whole block. To reach a line inside, use the Block Editor, or hold Ctrl while clicking.
It belongs to a group. Clicking one member brings the rest along. PICKSTYLE governs that, and the way round it is in our article on groups in AutoCAD.
Its layer is off or frozen. In that case it is not displayed at all, so this is no longer a selection question.
One point worth knowing for anyone writing lisp: the ssget function called from LISP does not honour layer locking. On a drawing with one layer locked — the lock bit reads correctly in the layer's group code 70 — ssget still returns all six lines. A lisp routine that selects and erases will therefore erase objects on the layer you thought was safely locked. Loading and reading a lisp file is covered in our article on the APPLOAD command in AutoCAD.
The selection commands and where to start them
Read straight out of the acad.cuix interface file of the 2027 release.
| Command | Alias | Ribbon | Menu |
|---|---|---|---|
QSELECT | none | Home → Utilities → Quick Select | Tools → Quick Select |
FILTER | FI | none | none |
SELECTSIMILAR | none | none | none |
SELECT | none | none | none |
LAYLCK | none | Home → Layers → Lock | Format → Layer tools → Layer Lock |
LAYULK | none | Home → Layers → Unlock | Format → Layer tools → Layer Unlock |
The four commands in the middle have no button anywhere on the ribbon or the menus, so typing the name is the only way in.
QSELECT is the one worth learning. It selects by property rather than by position: every line on a layer, every piece of text 2.5 high, every circle under radius 100. On a real production drawing it beats dragging boxes by a wide margin.
Nine variables that govern selection
Values read on the 2027 release with nothing changed.
| Variable | Value | What it governs |
|---|---|---|
PICKADD | 2 | Whether a new pick adds to the set or replaces it |
PICKAUTO | 5 | Whether clicking empty space opens a box |
PICKBOX | 3 | Radius of the pick aperture in pixels |
PICKDRAG | 2 | Box drawn by two clicks or by holding the button |
PICKFIRST | 1 | Whether you may select before calling a command |
PICKSTYLE | 1 | Whether picking one member brings the whole group |
SELECTIONPREVIEW | 3 | Objects highlight as the cursor passes over |
SELECTIONCYCLING | 0 | Whether overlapping objects raise a prompt |
LAYLOCKFADECTL | 50 | How far objects on a locked layer are faded |
The pickadd variable at 2 is where older guides go wrong. A value of 2 means each pick adds to the set, and holding Shift removes. Set it to 0 and every pick replaces the last, which is exactly when people complain that "picking this one loses that one". Any guide still saying the default is 1 was written against an older release and never rechecked.
SELECTSIMILARMODE reads 130, which is another bitcode worth splitting: 130 = 2 + 128. Autodesk's page for the variable gives 2 as Layer and 128 as "Name, for referenced objects including blocks, xrefs, and images". So picking one door block and running SELECTSIMILAR gathers every door of that name on that layer, and nothing else. On a plan holding several hundred blocks that is the difference between one command and an afternoon of clicking.
SELECTIONCYCLING at 0 means that when two lines sit exactly on top of each other, the program takes one without asking. Set it to 2 and it offers a list — well worth switching on for drawings that arrive from elsewhere. Overlapping linework is covered in our article on removing duplicate lines in AutoCAD.
Removing objects from a selection
Esc drops the lot. The more useful trick is dropping a few items out of a set you already have: hold Shift and click the ones to remove. Hold Shift and drag a box to remove a whole cluster.
At the Select objects: prompt there is another route: type R to switch to remove mode, and A to go back to add mode.
Three things people say that are not true
| What people say | What the 2027 release actually does |
|---|---|
| A selection box is a selection box, only the colour differs | The same box over the same six lines: a window catches 3, a crossing catches 6 |
PICKADD defaults to 1 | It reads 2 |
| A locked layer protects objects from lisp as well | ssget called from LISP still returns objects on a locked layer |
Frequently asked questions
What is the quickest way of selecting objects in AutoCAD on a busy drawing?
Not a box at all. QSELECT picks by property, so one command takes every line on a layer or every piece of text at one height, however scattered they are.
Which box catches everything?
Drag right to left, which gives a crossing, green fill. It takes anything the box touches.
Why does clicking a line do nothing?
Usually its layer is locked. Objects on a locked layer are faded and hovering shows a padlock. Type LAYULK to unlock.
Picking a new object loses the one I had?
PICKADD is set to 0. Setting it back to 2 restores adding.
Is there a way to select by property rather than position?
Yes, type QSELECT. It selects by layer, by colour, by object type, by text height.
Two lines sit exactly on top of each other — which gets picked?
One of them, without a prompt, because SELECTIONCYCLING is 0. Set it to 2 and the program offers a list.