Your DWG isn't broken. It's just not a drawing. It's a database of geometry that AutoCAD happens to render as lines, and when you hand that database to Illustrator, Illustrator does the only honest thing it can: it draws every single entity. Every hatch stripe is a path. Every arc that got written out as a polyline is forty paths. Every dimension string is a little constellation of tick marks, leader lines and outlined letterforms. Nothing has gone wrong. You asked for everything and you got everything.
So the fix isn't a magic import setting. The fix is deciding — before you export — how much of that database you actually want, and then controlling what survives by layer rather than by object. Do that and the Illustrator side takes twenty minutes. Skip it and you'll spend an evening shift-clicking individual hatch lines and still end up with a diagram that looks like it was drawn by a photocopier.
Four things account for nearly all of it, and knowing which one is biting you decides your strategy.
Hatch patterns. A solid hatch is one filled region. A pattern hatch — brick, concrete, hardcore, the diagonal one everybody uses for "existing" — is not a fill at all. It's a dense bundle of individual line segments generated to fill a boundary. One room of floor hatch can carry more paths than the entire rest of your plan. This is the single biggest cause of a 40MB Illustrator file that scrolls like it's underwater.
Curves that got flattened. Depending on how the file was authored and exported, arcs, circles and splines can arrive as polylines made of short straight chords. Zoom in and your lovely curved wall is a thirty-sided polygon. Worse, each chord may be a separate path, so you can't just select the curve and restroke it.
Text and dimensions. SHX text in particular tends to arrive as outlined geometry — not editable type, just shapes of letters. Dimension strings arrive as their component parts. You get hundreds of fragments that are no longer text and no longer useful, and you can't retype them.
Blocks and nested blocks. A tree block placed two hundred times doesn't arrive as two hundred instances of one thing. Each one typically lands as its own group of paths, so changing the tree means changing it two hundred times.
Notice what these have in common: all four are fixable upstream, and none of them is fixable quickly downstream.
Do the Surgery in CAD, Not in Illustrator
This is the part the tutorials skip, and it's the part that saves the evening.
Work on a copy of the DWG. Call it something like plan_FOR-ILLUSTRATOR.dwg so nobody ever confuses it with the issued set. You are about to delete things on purpose.
Then, roughly in this order:
Delete what a diagram doesn't need. Dimensions, grids, setting-out text, title block, revision clouds, section marks, levels, drainage runs, the furniture nobody will see at diagram scale. Be brutal. A presentation plan needs walls, openings, a few key furniture pieces, maybe a floor boundary. That's it. Everything you delete here is a path you don't have to find and select later.
Deal with hatches deliberately. Either freeze the hatch layers entirely and add fills in Illustrator (almost always the right call — Illustrator's pattern fills and live paint are far nicer anyway), or keep only the one hatch you genuinely need and accept the path count for that one.
Purge and audit. Run PURGE to strip unused blocks, layers and linetypes, then AUDIT to clean errors. This doesn't reduce visible geometry much, but it stops the file carrying a lot of invisible baggage into Illustrator.
Kill duplicates. Drawings that have been worked on by three people for two years are full of lines drawn exactly on top of other lines. AutoCAD's OVERKILL command removes duplicate and overlapping geometry. If your plan feels inexplicably heavy for how simple it looks, this is usually why.
Get your layers right, because layers are your only handle later. Everything you will want to control as a group in Illustrator must be on its own layer in CAD. Walls cut, walls beyond, floor, furniture, glazing, external. If your CAD file is organised by colour rather than by layer — plenty of older files are, with everything on Layer 0 and line weight carried by colour — then map it properly before you export, or you will arrive in Illustrator with one layer and no way to select by category.
For Revit, the same logic applies through the DWG export dialogue: export a view, not the model, and set the layer mapping so each category lands on a sensibly named layer. Export the view you've already turned things off in. A cleaned-up Revit view exports as a cleaned-up DWG.
Importing Without Flattening Everything
File > Open the DWG rather than Place it, so the layers come through as Illustrator layers. Set the scale on import if you need measurable output; if the drawing is going on a board, honestly, scale it visually to the layout once and stop worrying — nobody dimensions off a presentation plan.
Two things to check the second it lands:
Open the Layers panel. If you see one layer, something went wrong in the export mapping and it's worth going back rather than pushing on. If you see your named layers, you're in business — everything from here is per-layer work.
Switch to Outline mode (Cmd/Ctrl+Y). You'll see the true path structure without fills and strokes flattering it. This is where you find out whether your curves are curves or thirty-sided polygons, and whether that "line" is one path or sixty.
Control Line Hierarchy Once, Not Object by Object
Here's the mental shift. In CAD you think in line weights per layer. In Illustrator, do exactly the same thing — but using the layer's own appearance, not the objects inside it.
Click the target circle to the right of a layer name in the Layers panel. That targets the layer itself. Now set a stroke weight and colour. Everything in that layer takes it, and anything you draw into that layer afterwards inherits it too. Change your mind about the cut line weight at eleven at night? One click, one number, whole drawing updates. That's the entire game.
Save each of those as a Graphic Style — cut wall, wall beyond, furniture, hairline detail — and you have a reusable line-weight hierarchy you can drop onto the next project's import in about a minute.
When the import hasn't come through on clean layers, Select > Same is your rescue tool. Click one line, then Select > Same > Stroke Colour (or Stroke Weight, or Fill & Stroke). Every object sharing that attribute selects at once. Because CAD colour usually corresponded to pen weight, this effectively reconstructs your line hierarchy from colour. Select them all, drag them into a new named layer, and you've rebuilt the layer structure the export lost.
For the repeated elements — trees, cars, people, that one chair — convert one instance to a Symbol and replace the rest with instances. Edit the symbol once and all two hundred update. Same logic with Brushes: make a scatter brush of your tree and a hedge becomes a stroke you can redraw rather than a cloud of fragments.
And be careful with Object > Path > Simplify. It works, but it works on everything you've selected with the same tolerance, and a tolerance that tidies a flattened curve will also round the corner off a wall junction. Use it on selections of curved geometry only, with the preview on, and nudge the slider until the path count drops but the shape doesn't move. Object > Path > Clean Up is the safer one — it removes stray points and empty text paths, and it can't damage anything you wanted.
The Honest Option: Don't Import the Geometry at All
For presentation drawings, there's a faster route, and it's what we teach in the course: export the CAD view as a PDF, open that in Illustrator, select everything on that layer, drop it to about 50% opacity, lock the layer — and then redraw over the top on your own named layers with the pen tool.
This sounds like more work. It is almost always less.
A presentation plan has maybe a tenth of the information your construction DWG carries. Tracing it gives you clean single paths, correct corners, your own layer structure from the start, closed shapes you can actually fill, and curves that are curves. No hatch archaeology, no orphaned dimension fragments, no eighty-sided circles. Lay out walls, then columns, then furniture, then doors, windows and flooring, then the details — each on its own layer — and by the time you're finished you have a drawing that is genuinely yours and genuinely editable, not a repaired corpse.
The repair route is right when the geometry is complex and accurate and you need it exactly — a site plan with real survey boundaries, an urban diagram with hundreds of building footprints. The trace route is right for almost everything that goes on a board.
Keeping Illustrator Responsive
If the file is already heavy: work in Outline mode while you draw, hide layers you aren't editing, and delete the base layer entirely once you've finished tracing over it rather than just switching it off. Purge unused swatches, brushes and symbols from the panels before saving. And split genuinely huge drawings — a masterplan, say — into separate documents by zone, then place them into one layout. Illustrator is much happier managing three linked files than one enormous one.
As for the conversion plugins and auto-tracing services: they're built for turning raster images into vectors. If you already have a DWG, you already have vectors. Running them through a tracer adds a generation of error for no gain.
Why This Matters the Moment It Prints
At A0, raster lets you down in a specific and humiliating way. An ISO A0 sheet is 841 × 1189mm. At the 300dpi that print bureaus conventionally ask for, that's roughly 9,900 × 14,000 pixels — about 140 megapixels of image. Your Photoshop diagram is almost certainly not that, so it gets scaled up, and scaled-up linework goes soft and grey exactly where it needs to be sharp and black.
Vector doesn't care. A 0.25mm stroke is 0.25mm on an A4 proof and 0.25mm on the A0, resolved at whatever the plotter can physically put down. Text stays type. You can change the cut-wall weight after the crit and reprint in ten minutes. And when the same diagram needs to be a thumbnail in your portfolio and a full-bleed sheet on the wall, it's one file doing both jobs.
Get the pipeline right once and you stop thinking about it. The CAD file is cleaned and layered. The import lands on named layers. Line hierarchy lives in layer appearances and graphic styles. Repeated elements are symbols. After that, the drawing is a drawing again — something you can argue with, change, and print at any size without flinching.
Stop wrestling the DWG. Decide what you want from it, take only that, and rebuild the rest properly.
