Props & placements
A prop system holds a set of props and a rule for where they go. You create one by picking a placement in one of four columns, fill it from the library, and bind it to the elements you select in the viewport.
What a prop system is
A prop system is one card in the Props section that holds a set of props and a rule for where they go. The card is the unit you edit; the props inside it are a pool the city draws from, not one object placed by hand.
Props sits in the DESIGN module, in each editing mode that dresses something — Roads, Blocks (which picks regions), Lots and Massing. The section is closed when you arrive; only Materials opens by itself. Open Props and you get the cards the theme already made for whatever you have selected, then your own systems below them, then a + to make a new one.
The iCity Editor in DESIGN, Roads mode, one road segment selected in the viewport. The Props section expanded, showing the theme's own collapsed cards at the top, one user system card below them, and the + button labelled 'Create a prop system' at the foot of the section.
A system does nothing until two things are true: it holds at least one prop, and it has been assigned to at least one element. Until both hold, the card's options panel stays hidden, because there is nothing for the numbers to act on.
Props ride on the dressed city, not on the draft. If you have not dressed the city yet, do that first — see Themes.
The four kinds
Every system is one of four kinds, and the kind is fixed when you create it. Switching it later would strand whatever the system had already bound under the wrong distribution, so the picker asks once and does not offer a change afterwards.
Distribute and Packed offer the same placements and differ only in whether instances may overlap, which is why one surface placement appears in both columns. The card's top-right corner carries a type indicator showing which kind you are looking at.
Creating a system and picking a placement
Press the + at the foot of the Props section. A menu titled Place props… opens with four columns, one per kind, and each column lists the placements this editing mode can dress that your scene actually carries. Picking one creates the system and closes the menu.
The four-column 'Place props…' menu open over the iCity Editor in Roads mode, with the column headings Path, Distribute, Packed and On Point visible and the road and sidewalk placements listed under them.
A placement is a named part of an element. In Roads the live ones are Road surface, Road bounds, Crossing, Sidewalk path, Sidewalk node and Sidewalk surface. Buildings carry Roof surface, Roof edge and Walls; lots and parks carry Green lot surface, Park surface, Park path and Urban path. Nothing is listed unless something in the scene can produce points for it, so the menu is short on purpose.
If the city has never been dressed there is nothing to offer, and the menu shows a box reading “No instancer groups yet”. The two lines under it tell you to run the linker from a Pipeline > Linker menu; ignore them, that is a developer panel and no such menu is drawn for you. Dress the city and open the menu again.
The 'Place props…' menu on an undressed city, showing only the info box that reads 'No instancer groups yet' with the two lines beneath it.
The + tooltip reads “Create a prop system — scatter many, or Single to place one”. The picker no longer offers Single; systems saved by older builds keep their single card and its Grab button.
Putting props in a system
Open the card's objects panel and press its +. The asset browser opens on props, in multi-select: click as many cards as you want, then press Assign. Each picked prop is imported into the system's own hidden source collection and gets its own row on the card.
The iCity asset browser opened from a prop system's objects +, in assign mode with three prop cards selected, the category sidebar showing its checkbox tree, and the footer reading 'Assign 3'.
The sidebar is a category tree with checkboxes; checking a parent also matches everything under it, and checking nothing shows everything. The categories are the taxonomy's own, 106 of them in eleven groups.
The three Surface and scatter categories are drawn in Surface details, not here, so a card for litter or cracks appears in that section instead.
Props with no 3D model
A prop the browser will not assign is a prop whose folder holds no model file — nothing ending in .glb, .gltf, .blend, .fbx or .obj. Only its preview image exists. Assigning one used to yield a flat plane wearing that image, so the browser now refuses.
Such a card carries a red ! in the top-right of its preview. Click it and the footer explains: a panel titled No 3D model reading “This prop is only an image. Generate a 3D model from it with AI, or pick a different prop”. In the action row, Assign is replaced by Generate Model and a red No 3D model label appears beside it.
The asset browser with a single image-only prop card selected. Visible: the red ! badge on the card preview, the 'No 3D model' explanation panel, and the footer row where the accented Generate Model button and the red 'No 3D model' label have replaced Assign.
With several picked, the gate reads the whole set. Assign stays available as long as something in the selection can be assigned, and the model-less ones are silently dropped at commit — the log says how many were skipped. The label then reads the count, for example “2 of 5 have no 3D model”, and the button becomes Generate 2 Models.
Generate Model only works on assets that came from the cloud. A prop you added yourself from a folder has no cloud identity, so the button prints that and sends nothing. To get a usable model for your own image, generate a prop from it instead — see Generating a single material or prop and Your own assets.
Binding a system to selected elements
A prop system in an editing mode is not drawn in the viewport. It is assigned to the elements you select, because a per-element binding is the only channel the dressed city exposes.
- Select one or more elements in the viewport — shift-click to add to the selection.
- Press Assign selected on the card. It lights up once the system holds props and sits on nothing yet, and its tooltip names what it is about to do: “Put this system's props on the N selected element(s), at N placement(s)”.
- Read the status line under the buttons: 3 element(s) · 3/3 bound — how many of the system's element-by-placement pairs actually took.
A user prop system card with props in it and two road segments selected. Show the Assign selected / Remove selected pair, the eye, camera and × icons to their right, and the grey status line below reading 'N element(s) · N/N bound'.
Remove selected takes the system off only the elements you have selected, so a system on twenty roads can be pulled off one of them without losing the other nineteen. It is inert when the system is not on your selection, and says so. The × at the end of the row deletes the system outright.
The card header carries one small toggle per sibling placement — the other placements in the same column that this mode can dress. Ticking one spreads the same system onto that placement as well; the tooltip reads “Also place on <placement> — toggle (several can be on at once)”. An On Point system offers none, because a cloud's exact points are not a set you can spread.
Buttons that need a selection say why when they are inert: “Select an element in the viewport first”. A system made before the placement picker existed cannot be assigned at all and reads “This system predates the placement picker — make a new one to assign it”; make a fresh system instead.
Tuning a system
Once a system holds props and sits on an element, an options row appears on the card. Its header carries the everyday numbers so you rarely need to open it: Spacing, Offset and Depth for a path system, Density, Margin and Seed for a surface one.
A path prop system card with its options panel expanded, showing the Spacing, Offset and Depth sliders and the Align row with its 'To tangent' and 'To normal' buttons.
- —Align sets the frame each instance is placed in. To tangent (path systems only) faces each prop along the path; To normal stands it up along the surface normal instead of straight up.
- —Each prop row in objects carries its own copy of the distribution numbers, seeded from the system's, plus Turn and Random — a fixed yaw and a random spread around it. A bench can face along the path while the bin beside it does not.
- —The eye and camera icons on the card hide the whole system in the viewport or in renders; the same pair on a prop row hides that one prop.
An On Point system has no distribution sliders at all: one prop per point, and the points are given.
The cards the theme made
The cards above your own are the ones the dress built for whatever you have selected — one per element, placement and category, named like Sidewalk path - bench. They start collapsed and are scoped to your selection, so a road shows its own handful rather than the city's hundreds.
They behave like your systems with two differences: their + links a prop the library step already built rather than importing a new one, and their Assign selected gives every selected element the same props for the same placement and category. Their numbers are the live bake values, so changing one re-bakes that part of the dress.
A re-dress rebuilds the city's node groups and re-initialises every binding. Opening the Props section re-states every assigned system's bindings, which is why your props come back rather than disappearing after a sync. See Re-dressing after a change and What survives a re-dress.
Systems that scatter over a shape you draw rather than over a city element live elsewhere: Scatter mode (Alt+6, DESIGN only) for free-standing systems, and Surface details for wear and imperfections.
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