September 2026 — Week 2 of 9

Applied Spatial Analysis Using QGIS - Permanent Metric Transformation

Applied Spatial Analysis Using QGIS — GIS for Surveyors (2026 Cohort) · 20 Sep 2026 · 24:20 · Watch on YouTube (offline-safe)

Do live (this session): reopen Week 1 in WGS84 → create two layers by digitizing (a LineString and a parks polygon layer) → permanently reproject them to UTM 36N → prove it in a fresh project → add an area field with $area.
Data: none imported this week — we create it from scratch  |  Deliverable (graded): your LineString + parks layers in UTM Zone 36N (EPSG:32636), units = metres, with an area field = $area in square metres — screenshot to WhatsApp Course_Helpers.

I write this after every live session — so students who lost power or signal can catch up in minutes, and so our community has a searchable archive for the future. Last week we imported data into QGIS. This week we did something bigger: we created data from nothing, and we made it measurable.

This week's one question: "My map is drawn in degrees — how do I get data I can measure, in metres?"

Why Week 2 Exists

Last week we brought our sample CSV and GPS files into QGIS — raw field points and context layers, everything in WGS84 (EPSG:4326), units = degrees. Degrees are great for locating a place on the globe, but they are useless when you need distances, buffers, or areas.

Week 2 answered the next question: how do I go from "drawn on a map in degrees" to data I can actually measure in metres? And while we were at it, we created our first data from scratch — not imported, drawn.

The plan, live on screen:

  1. Open last week's project — everything in WGS84
  2. Create two layers by digitizing: a linear feature and a polygon feature (parks)
  3. Reproject them permanently from WGS84 to UTM Zone 36N in metres
  4. Close QGIS completely, open a new project, add the projected layers — prove the map now reads EPSG:32636 in metres
  5. Add an area field to the parks layer with the Field Calculator and $area

1) Recap — Everything Is Still in Degrees

We opened the project from Week 1: the sample CSV and GPS layers, all sitting in WGS84 (EPSG:4326) — geographic, degrees. That was the right choice for Week 1: import and alignment first.

But degrees have no fixed length. One degree of longitude near Sudan is a different real-world distance than one degree near the equator. So before we can measure anything honestly — distance, buffer, area — the data must be in metres.

2) Creating Data From Scratch — The Digitizing Toolbar

This week there was no input file to import. We made our own data:

Layer → Create Layer → New GeoPackage Layer. Before drawing anything, set three things:

Then add the attribute fields that every road or park feature will carry:

Layer Geometry Fields added
Linear feature (e.g. roads) LineString name, remarks, created_by, created_date
Parks Polygon name, type, remarks, created_by, created_date

With the two empty layers ready, we switched on editing (the pencil icon) and used the digitizing toolbar to click the features straight onto the map. Drawing your own data is the foundation of cadastral work: you are not importing someone else's map, you are building the map.

Tip: pick the geometry type for the question — LineString for anything linear (roads, rivers, pipelines), Polygon for anything with area (parks, plots, districts).

3) Permanent Reprojection — Degrees to Metres

A map canvas can reproject on-the-fly — it just redraws things so they look right. But the data itself is still stored in degrees. To measure, we need a permanent change.

Vector → Data Management Tools → Reproject Layer, target CRS WGS 84 / UTM Zone 36N (EPSG:32636). South Sudan sits inside UTM zone 36N, so this is our metric zone.

The result is a brand-new layer, stored permanently in metres. The original WGS84 layers stay untouched — we did not destroy the source, we created projected copies. This is the difference between "it looks projected" and "it IS projected".

4) Prove It — Close, Reopen, Fresh Project

Faith is not enough in GIS — verify. We closed the application completely, opened a new QGIS project, and added the reprojected layers with Layer → Add Layer → Add Vector Layer.

Two confirmations on the canvas:

If you only remember one habit from this week: a permanent reprojection is proven by reopening in a fresh project and reading the CRS and units yourself.

5) Area in Square Metres — the Field Calculator and $area

With the parks layer in metres, area finally makes sense. We opened the attribute table, entered editing mode, opened the Field Calculator, created a new field area, and set its expression to:

$area

$area returns the area of each polygon in the layer's CRS units. Because the layer is now UTM 36N, that answer is in square metres — exactly what a land manager needs.

Tip: use round($area, 2) for cleaner, report-friendly numbers. And remember — $area is only meaningful after the reprojection in step 3; run it on a degrees layer and you get nonsense.

We saved the edits, wrapped up with a recap, and answered questions on the open floor.

What We Did Live — Scrub Guide

Minutes are better spent clicking QGIS live than re-reading theory. Replay the demo at 1.25x if you missed a click.

Common Hang-ups and Fixes

  1. Still reading degrees after reproject: you are looking at the original WGS84 layer. Find the new reprojected layer and check its CRS — it should say EPSG:32636.
  2. $area gives tiny or fractional values: the layer is still in WGS84 degrees. Run the reprojection first, then calculate $area.
  3. The path "already exists": you are reusing a layer/table name from an earlier try. Save to a new name or folder.
  4. Fields missing after creation: attributes can be added any time — open the attribute table → Field Calculator, or add a column in the layer properties.

What You Should Have Now

This is Project 1B. One quiz plus one practical lab — graded.

Chapters (from the recording — 24:20)

00:01:15  Welcome & this week's mission
00:02:00  Live demo - Digitizing a new Line & Polygon layer
00:11:20  Layer Re-projection from WGS84 to UTM 36N in metres
00:21:45  Adding the "Area Field" in the parks layer (Field Calculator, $area)
00:24:19  Recap & the week's deliverable

What's Next

Week 3 — Cadastral Boundary Mapping & Topology (Project 2): we move from drawing features to making them correct — land parcels, topology checks, and boundaries that behave. Bring your parks and LineString layers in UTM 36N. Every Sunday 9:45 a.m.

Resources: YouTube playlist Applied Spatial Analysis Using QGIS — Live Sessions & Labs · Video: Week 2 on YouTube · Course site saltco.org · Software QGIS (free & open source, offline) · Full publish kit in recordings/zoom_recordings/02_WEEK2/

Did I miss something? Tell me in the Q&A or open an issue — this archive is living and I will update it. — Sallah