Skip to main content

Relations and repeat observations

Outcome: create and test a GeoPackage relation connecting one stable monitoring site to many observation records.

A common GIS mistake is to create a new point every time somebody revisits the same site. A better model separates the site from visits.

monitoring_site
  site_id
  geometry
       |
       | 1 : many
       v
observations
  observation_id
  site_id
  observed_at
  condition

Create the tables​

In a GeoPackage use:

monitoring_sites — point geometry, one row per stable site
observations — no geometry required, many rows per site

Use text IDs that remain stable across exports.

Define the relation​

Open Project → Properties → Relations and add a relation:

  • referenced/parent layer: monitoring sites
  • parent field: site_id
  • referencing/child layer: observations
  • child field: site_id

Give the relation a descriptive ID/name.

Use forms​

With a relation configured, a site form can display its related observation records. This is useful for repeat taiao monitoring, marae asset inspections and historical evidence tables.

Do not force one-to-many into a join​

A normal QGIS layer join is one-to-one in practice. If a site has 20 visits, the data model should contain 20 child rows rather than 20 copies of the point or 20 date columns.

Exercise​

This exercise creates one point layer, creates a small teaching table and connects them. Allow about 15 minutes. The records below are synthetic and exist only to demonstrate the relation.

Use these two monitoring sites:

site_idrestoration_idsite_typestatusnotes
SITE-001REST-001repeat_photoactiveSynthetic example
SITE-002REST-002condition_checkactiveSynthetic example

Create these initial child observations:

observation_idsite_idobserved_atcondition_categorynotes
OBS-001SITE-0012026-02-14 10:00baselineSynthetic example
OBS-002SITE-0012026-08-12 10:00follow_upSynthetic example

1. Create the GeoPackage​

  1. Open a new QGIS project.
  2. Set the project CRS to NZGD2000 / New Zealand Transverse Mercator 2000 (EPSG:2193).
  3. Choose Layer → Create Layer → New GeoPackage Layer.
  4. Browse to a working folder and create awa-relations.gpkg.
  5. Set Table name to monitoring_sites and Geometry type to Point.
  6. Add these text fields: site_id, restoration_id, site_type, status and notes.
  7. Click OK.

2. Add the two teaching sites​

  1. Select monitoring_sites in the Layers panel and click Toggle Editing.
  2. Click Add Point Feature and place a point anywhere in the map canvas.
  3. Enter the SITE-001 values from the table above.
  4. Add a second point using the SITE-002 values.
  5. Save the edits and turn editing off.

The point locations are arbitrary teaching geometry. Do not interpret them as real monitoring sites.

3. Create the observations table​

  1. Choose Layer → Create Layer → New GeoPackage Layer.
  2. Select awa-relations.gpkg.
  3. Set Table name to observations and Geometry type to No geometry.
  4. Add fields for observation_id, site_id, observed_at, condition_category and notes.
  5. Add the two observation rows shown above.
  6. Save the edits.

4. Define the relation​

  1. Choose Project → Properties → Relations.
  2. Click Add Relation.
  3. Set the name and ID to site_observations.
  4. Set Referenced (parent) layer to monitoring_sites and its field to site_id.
  5. Set Referencing (child) layer to observations and its field to site_id.
  6. Click OK, then Apply and OK.

5. Confirm it works​

  1. Select monitoring_sites and use Identify Features to click the SITE-001 point.
  2. Open its feature form if it is not already displayed.
  3. Find the site_observations related-record section. It should contain OBS-001 and OBS-002.
  4. Add a child observation with a new unique ID such as OBS-003, set site_id to SITE-001, and save it.
  5. Reopen the site form and confirm that three observations now appear while the parent point remains a single feature.

If no records appear, compare the site_id values exactly. Spaces, different capitalisation or a missing ID will prevent the match.

Check​

  • parent IDs are unique
  • every child site_id exists in the parent table or is deliberately flagged unmatched
  • visit date/time is stored as a proper field
  • deleting a site is handled cautiously because child records may remain

See the Awa restoration worked example for the same stable-site/repeat-observation pattern in a fuller project.

Next: Models and batch processing.

Official reference: QGIS joins and relations.

Last reviewed: 3 September 2026

Last updated on