Backdrop Digitalisation — Recipe (QGIS)

Tool-bound implementation of the Backdrop digitalisation Task Schema.

Editorial note: the mechanics below (layer creation, edit mode, snapping, rings/holes) are grounded in the transcript of your “basic GIS operations in QGIS” video, supplied manually. That video covers general QGIS digitising over an OpenStreetMap basemap — it does not itself demonstrate reconciling hand-drawn field notes against an aerial photo, so that part of the write-up is a general reconstruction pending a source specific to backdrop digitalisation.

Load the backdrop

Add the orthophoto — as a WMS/WMTS connection or a local raster layer — and zoom to the extent of your study area. If it isn’t already georeferenced, see Georeferencing (Recipe - QGIS) first.

Build the empty layer (Task Schema step 1)

Layer → Create Layer → New GeoPackage Layer: browse to (or create) your project’s .gpkg file, name the table after the entity — not after the GeoPackage itself, which QGIS will otherwise default to — set the geometry type, and set the coordinate reference system (in Denmark, searching the EPSG code directly, e.g. 25832 for ETRS89 / UTM zone 32N, is faster than browsing the list). Add the attribute fields to match your Attribute Framework exactly before dismissing the dialog.

Digitise (Task Schema step 2)

Toggle the layer into edit mode using the pencil icon on the Digitizing toolbar, then use the corresponding Add Point / Add Line / Add Polygon Feature tool. Place vertices by clicking, and right-click to finish the feature — this immediately opens its attribute form, which you fill in directly from your field notes.

Interior exclusions (rings/holes): enable Advanced Digitizing, digitise the outer boundary as normal and finish it, then use Add Ring on that same feature to cut the interior hole. QGIS treats a ring as a hole precisely when the outer and inner boundaries belong to the same feature — a second, separately-owned polygon placed on top is not the same thing.

Enforce boundary topology (Task Schema step 4)

The magnet icon on the Snapping toolbar toggles snapping on; the settings beside it let you choose whether to snap to vertices, edges, or segments, and set a tolerance. Enable snapping before digitising the second of two features that must meet exactly, not after.

Save and close out (Task Schema step 5)

Once digitising is complete, do a final pass comparing the digitised layer against your original field notes.

ArcGIS

(To fill in: the equivalent layer-creation/editing/snapping workflow in ArcGIS Pro — same Task Schema, different interface.)