GEOG 380 - Lab 07

DEM Analysis

What does DEM stand for?

Digital Elevation Model

What does a DEM store?

Elevation values for each raster cell.

What type of data structure is a DEM?

A raster

What was the DEM resolution used in this lab?

90 m

What mission provided the DEM used in the lab?

Shuttle Radar Topography Mission (SRTM).

What is terrain analysis?

Extracting information from elevation data to understand and visualize landforms.

What are common outputs derived from a DEM?

Hillshade, slope, curvature, coloured elevation maps, and 3D scenes.

What is a hillshade?

A shaded-relief raster created by simulating light shining on terrain.

What is the main purpose of a hillshade?

To make terrain shape and relief easier to see.

What is traditional hillshade?

A hillshade created using one light source direction.

What is multidirectional hillshade?

A hillshade created using multiple light directions.

What is one advantage of traditional hillshade?

It gives a dramatic, realistic-looking relief effect.

What is one disadvantage of traditional hillshade?

Some features may be hidden in dark shadows.

What is one advantage of multidirectional hillshade?

It shows terrain more evenly and reveals more detail.

When is traditional hillshade more useful?

When you want strong visual relief and a dramatic appearance.

When is multidirectional hillshade more useful?

When you want clearer terrain interpretation and fewer hidden areas.

In the lab, what azimuth was used for traditional hillshade?

315°.

In the lab, what altitude was used for traditional hillshade?

45°.

What does slope represent physically?

The steepness of the land surface.

What does a low slope value mean?

The terrain is relatively flat.

What does a high slope value mean?

The terrain is steep.

What units were used for slope in the lab?

Degrees.

How does ArcGIS Pro calculate slope conceptually?

By comparing each cell’s elevation to surrounding cells to estimate local steepness.

What does slope measure: elevation or rate of elevation change?

Rate of elevation change.

What type of colour scheme is usually best for slope?

A sequential colour scheme.

Why is a sequential colour ramp good for slope?

Because slope values progress from low to high in one direction.

What is profile curvature?

The curvature of the land surface in the downslope direction.

What does profile curvature help describe?

Whether flow moving downhill tends to accelerate, decelerate, or stay steady.

What do profile curvature values near zero represent?

Nearly planar surfaces.

Why is profile curvature harder to interpret than slope?

Its units are less intuitive and relate to change in slope rather than angle.

What type of colour scheme is best for profile curvature?

A diverging colour scheme.

Why is a diverging colour ramp best for profile curvature?

Because meaningful values occur on both sides of zero.

What do negative and positive curvature values indicate?

Different types of surface bending or slope shape.

What does hillshade emphasize best?

Landform shape and visual relief.

What does slope emphasize best?

Terrain steepness.

What does profile curvature emphasize best?

The shape of the slope surface in the downslope direction.

Which is more quantitative: hillshade or slope?

Slope

Which is generally more analytical: slope or hillshade?

Slope

Why combine a hillshade with a coloured DEM?

To show both terrain shape and elevation at the same time.

What does the hillshade contribute in a combined display?

Relief and terrain texture.

What does the coloured DEM contribute in a combined display?

Elevation information

Why might a coloured DEM alone be less effective?

It shows elevation but can look visually flat.

Why might a hillshade alone be less informative?

It shows relief well but not exact elevation ranges.

What is usually adjusted to combine a colour DEM with hillshade effectively?

Transparency

What is a 3D scene in ArcGIS Pro?

An interactive visualization where layers are displayed over terrain in three dimensions.

What is the purpose of adding a DEM as an elevation source in a 3D scene?

To shape the ground surface according to elevation.

Why are 3D scenes useful?

They make it easier to understand terrain shape, relief, ridges, and valleys.

Which 3D scene was considered most effective for visualizing topography?

The 3D hillshade and coloured elevation scene.

Why is the 3D hillshade + coloured elevation scene effective?

It combines terrain shape from shading with elevation information from colour.

Which 3D product is more useful for steepness analysis than general visualization?

3D slope.

Which 3D product is more useful for terrain-form analysis than general visualization?

3D curvature.

Which lab product is best for general terrain visualization: hillshade, slope, or curvature?

Hillshade

Which lab products are best for analysis rather than simple visualization?

Slope and profile curvature.

What is the Z-factor used for in terrain tools?

To scale vertical elevation values relative to horizontal units.

What Z-factor was used in this lab?

1

When is a Z-factor of 1 appropriate?

When vertical and horizontal units are already consistent.

What does manual interval classification mean?

Choosing the class breaks yourself instead of using automatic classification.

Why use manual intervals for slope or curvature?

To make the map more meaningful and easier to interpret.

What kind of imagery was also used in this lab for visualization?

IKONOS imagery.

Was the IKONOS image mainly used for analysis or visualization in this lab?

Visualization

What is the difference between visualization and analysis in raster terrain products?

Visualization focuses on appearance and interpretation, while analysis focuses on measurable terrain properties.

Give one example of a visualization-focused raster product from this lab.

Hillshade

Give one example of an analysis-focused raster product from this lab.

Slope

What is the main conceptual difference between slope and profile curvature?

Slope measures steepness, while profile curvature measures how the slope surface bends.

What is the main conceptual difference between hillshade and slope?

Hillshade simulates lighting for visual relief, while slope measures steepness quantitatively.