ENCN205 — Lecture 09: Raster Analysis

Interactive Demo: DEM Explorer — Banks Peninsula (LINZ 8m DEM)
~10 min activity

DEM Explorer

Elevation, hillshade, slope, combined & flood analysis

View Mode

Opacity

Transparent 80% Opaque

Raster Info

Grid size:500 × 500 cells
Cell size:8 m
Coverage:4 km × 4 km (16 km²)
Elevation range:1 – 781 m
Current layer:Elevation
Click position:—
What is a raster? A grid of cells (pixels), each storing a numeric value. This is a real 8m DEM from LINZ covering part of Banks Peninsula — a volcanic landscape with steep valleys, ridgelines, and peaks up to 781m. Every cell holds an elevation in metres. Derived layers (hillshade, slope) are computed from the same grid using focal operations.

Guided Questions

Q1

Switch to Hillshade mode. Try each sun direction preset. Which sun angle best reveals the radial erosion valleys on the volcanic peaks? Why does sun direction matter for DEM visualisation?

Q2

Switch to Slope. Where are the steepest areas (red)? How do they relate to the volcanic peaks and erosion channels? Name one engineering application where slope data is critical.

Q3

This DEM has 500 × 500 cells at 8 m resolution. Calculate the total area covered in km². Show your working: Area = cols × rows × (cell size)².

Q4

What is the difference between local, focal, and zonal raster operations? Give one example of each that could be applied to this DEM.

Q5

If you resampled this 8 m DEM to 100 m cells, what terrain features would be lost? Which resampling method is appropriate for continuous elevation data vs. categorical land-use data?

Q6

Switch to Flood mode. Set the threshold to 50 m. How many cells are flooded and what area does that cover? Show the calculation using the formula: area = cell_count × 8². Now increase to 100 m — does the flooded area double? Why or why not?

ENCN205 Applied Data Analysis — GIS Component
University of Canterbury | Data: LINZ NZ 8m DEM 2012