Modes & the tool rail

The rail

The left edge of the iCity Editor is one vertical column with two groups in it. The top group is the mode tabs — one icon per editing mode, drawn as a radio column, with the active tab turning solid and extending right into the panel beside it. The group below it is the tools for whatever mode is active.

The Graph tab is separated from the rest by a gap. It is the whole-city input rather than one editable layer of the city, so it does not sit in the same run as Roads, Blocks, Lots and Massing.

Rail buttons are icons. Until a button's icon file loads it draws the first two letters of the tool's name instead, so a rail showing Se, Dr, Lo is the same rail with its art missing.

The six modes

Each mode owns one layer of the city and shows only the tools that act on that layer. Switch modes by clicking a tab or by pressing Alt and a number.

The shortcuts use Alt so that plain 1 through 5 keep Blender's own collection-visibility toggles. They are installed into Blender's Object Mode keymap and are gated on you actually doing iCity work in that window, so in an unrelated scene the keys fall through to Blender.

Scatter is the odd one. It is a Design mode by design — scattering is dressing, and Draft hides the collections it writes into — so Draft drops the tab from the rail. Alt+6 still sets the mode anyway, and in Draft that leaves the rail with no mode tab lit at all, because the tab it would light is not there, over a panel reading “Scatter lives in Design — switch modules to place props.” Press Alt+1 to Alt+5 to get back.

The status bar names the mode you are in and the key that reaches it, so the mapping is learnable while you work. It reads Roads (Alt 2), Lots (Alt 4), Massing (Alt 5) and — see the next section — Regions (Alt 3). Graph and Scatter hand the bar back to Blender, because they have no selection gizmos and no draw key.

Blocks or regions

The mode is called Blocks on the rail and in the mode list. Everywhere else in the interface the same thing is called a region: the tools are Draw Region and Draw Custom Region, and the status bar caption for the mode is “Regions (Alt 3)”. The empty state has not caught up either — it still says “No blocks yet” and “Blocks appear when roads enclose an area”.

Treat them as the same word. A region is the parcel a closed loop of roads encloses; a custom region is a free polygon you draw inside one. The glossary records which name belongs to which surface, and Regions covers what you can do with them.

Select is a tool

Select leads every mode's tool list, including the modes with no draw tools at all. It is the default: the state in which nothing else has claimed the viewport click, so the selection gizmos, the box drag, A, Ctrl+I and the element popup all work.

Clicking a tool that is already lit turns it off, and what “off” means depends on which tool it is.

• —Re-click a lit draw tool and you land back on Select, so a stroke never leaves the viewport in a state where clicks do nothing.
• —Re-click a lit Select and selection switches off entirely — clicks pick nothing, the right-click popup and A / Ctrl+I stop responding. That is the state for panning a dense city without grabbing things. The only thing on screen saying so is the unlit Select button.

The ⋮ menu on the selection header carries the same idea per mode, as a checkbox reading “Hide gizmos in <Mode>”. Selecting and editing is covered in Selecting & editing.

D toggles the current mode's primary draw tool without reaching for the rail: Draw Road in Roads, Draw Region in Blocks, Draw Lot in Lots, Draw Footprint in Massing. Graph has no draw tool, so D falls through to Blender there. Pressing D again toggles the tool back off, and Esc backs out of an armed tool before its first click.

Draw Footprint has a second gesture. Press and hold its rail button for about 0.6 seconds and a chooser opens for what the next footprint will be drawn as; a short click still just arms the tool. Its tooltip says so, ending in “hold to choose what to draw”.

The rail is inert while the engine is stopped

Every Draft tool dispatches work to the iCity engine, a separate process outside Blender. With the engine stopped the tool column is not built at all — the mode tabs stay, the tools below them are simply gone. The selection gizmos go with them, and the status bar is handed back to Blender rather than advertising keys that do nothing.

Graph is the exception. Its panel keeps working with the engine down — it is where you assign a mesh as the base graph, import OSM or open the references — and the start button is pinned to a bar at the foot of the column instead. In Roads, Blocks, Lots and Massing the panel shows only a centred note reading “The iCity engine is not running. Start it to edit your city.” with the start button under it. Either way the button is labelled Start Engine when the scene already has a graph object and Start with default scene when it does not.

The DRAFT / DESIGN toggle

The right of the editor header holds a two-position toggle between DRAFT and DESIGN. Draft is where you draw and edit the structure of the city. Design is where you dress it — theme, materials, props, imperfections, lane markings, scatter.

The toggle is locked until two things are true: you are signed in, and the scene holds a graph or generated content for Design to dress. When it is locked, hovering it says which condition is missing.

The lock is enforced rather than advisory. If you are in Design and then sign out, or the city is deleted, the module is forced back to Draft on the next rebuild of the header.

Switching to Design changes the rail in two ways. The first tab is relabelled Theme — it is the same Graph slot, repurposed to hold the theme composer — and Scatter appears as a sixth tab. The tool column does not appear at all in Design: structural drawing is Draft-only, and the Design tools live on the cards instead.

There is no second row of tabs. Design's column is one scroll: the identity card for whatever you have selected, then collapsible sections under it — the mode's own options, then Materials, Props and Surface details. Those are covered in Materials and Surface details; the Theme tab itself is in Themes.