Geometry that should connect must connect exactly — a main that ends a hair short of its junction, or two pressure zones with a sliver of gap between them, is wrong data that looks almost right. Snapping is how the editor makes "almost" impossible.
Snapping controls
When you edit a line or polygon layer, the panel shows a "Snapping" switch with two target checkboxes:
- "Vertices" — new clicks lock onto existing vertices. Use this to land a main exactly on a junction point or to reuse a boundary corner.
- "Segments" — new clicks lock onto existing edges anywhere along their length. Use this to attach mid-segment, or to run a new boundary flush along an existing one.
Turn both on for most connected work. If snapping grabs geometry you don't want — dense areas offer many candidates — narrow the targets or zoom in so the intended candidate dominates.
Watch the lock as you draw
Check each vertex as it lands, not at the end. Extending a "Distribution Mains" segment from a junction is the classic case: that first vertex should snap onto the junction, not sit a metre off it.
Shared borders between polygons
When you create a polygon next to an existing one, snapping along the neighbor's edge lets the new "Pressure Zones" polygon reuse the shared border instead of retracing it freehand: snap to the neighbor's corner vertex, follow its edge with "Segments" snapping engaged, and close your shape from the far side.
Check the shared edge while you draw it, not after. Fixing a sliver later means reopening a finished feature — and polygons that properly share a border stay consistent through every later edit.