Drawing Rules for Polygons (No Overlap, No Gaps, and More)

Drawing rules (formerly known as topology restrictions) help you draw clean, connected polygons. When rules are on, the Polygon Tool blocks points that would break a rule, and it can snap your shape to follow the borders of the polygons next to it. Use drawing rules when shapes must fit together with no overlaps and no gaps, such as zones, territories, districts, or land parcels.

Turn on drawing rules

In the toolbar, select the Polygon Tool.
In the tool panel, click Set Drawing Rules (No Overlap, No Gaps, etc..).
A dropdown opens. Check the rules you want to use.

Once at least one rule is on, the button label changes to show the active rules. For example: 2 rules (No Overlap, No Gaps).

Note: Drawing rules currently apply to polygons only.

The rules

No Self-Intersect

The polygon cannot cross over itself. If you click a point that would make an edge cross another edge of the same shape, the point is blocked and you will see Blocked: No Intersection.

No Overlap

New polygons cannot cross into polygons that are already on the map. If you click inside or across an existing polygon, the point is blocked and you will see Blocked: Would overlap. When you draw along a neighboring polygon, your edge snaps to and follows the neighbor's border, so the two shapes share the same boundary instead of overlapping.

Checking No Overlap reveals two extra options:

Auto Node (on by default). When a drawn point lands on a neighboring polygon's edge, that point is also inserted into the neighbor. Both borders then render through the exact same spot at any zoom.
Stay Within (on by default). Start a shape inside an existing polygon to use that polygon as a boundary fence you draw within. This is useful for splitting a large area into smaller zones. When Stay Within is off, starting or drawing inside an existing polygon is blocked, and you will see Blocked: outside the boundary (Stay Within) if you try to leave the fence.

No Gaps

Prevents thin gaps between your new polygon and its neighbors. If your drawing touches a neighboring polygon's border in two places, the section between those touches snaps onto the neighbor's border exactly. No sliver of empty space is left between the two shapes.

When a point is blocked

If a click would break an active rule, the point is not added. A red marker appears at the blocked spot with a short message that names the rule, for example Blocked: Would overlap. Move the cursor to a valid spot and keep drawing.

Check a finished map with Validate Geometry

The Validate Geometry button at the bottom of the drawing rules dropdown opens the Geometry Validator. It scans the whole map for geometry problems, even on shapes drawn before you turned on drawing rules. You can also open it from the main menu (Validate Geometry) or from the command menu.

Click Validate Geometry. The Geometry Validator panel opens.
(Optional) Check Only selected to scan only the shapes you have selected.
(Optional) Use the filter checkboxes to choose what to look for: Validity, Overlaps, Slivers, Gaps, and Near Edge. All are on by default.
Click Scan.

The panel lists every issue it finds, such as:

Self-intersection: a shape crosses over itself.
Duplicate node: two points of a shape sit on the exact same spot.
Spike / needle vertex: a point forms a thin spike that sticks out of the shape.
Sliver polygon: a shape so thin it is likely a drawing artifact. The row shows its area.
Overlaps "...": two polygons overlap. The row names the other polygon and shows the overlapping area.
Gap between polygons: a thin empty space between polygons that should touch.
Vertex near edge but not on it: a point sits just off a neighbor's border instead of exactly on it. The row shows the distance.
Polygon has too few points: the shape does not have enough points to form an area.

Working with the results:

Click a row to zoom to the problem. The shape is highlighted and selected, and a marker shows the exact spot.
Click Fix on a row to repair it automatically. Fix is available for duplicate nodes, spike vertices, slivers, near-edge vertices, and shapes with too few points. Fixes can be undone with Undo.
Check Draw errors to draw each overlap, gap, and sliver as a red shape on the map, inside a folder named "Geometry Errors". Uncheck it to remove them.

When the map is clean, the panel reports No geometry errors found.