11 Visualizing terrain & Topographic maps

What are characteristics of terrain?

elevation (height with respect to vertical datum plane e.g. ellipsoid)

relief (changes in elevation, = slope gradient)

How can elevation be measured?

How can elevation be represented digitally?

representation of bare-earth terrain without vegetation or manmade features

What are historical terrain depitctions?

Before - 1800 (A):

• stylized hills and mountains

• bird eye viewsof terrain on maos

• block diagrams, orthographic views, contour lines, hachures

After - 1800 (B):

• shaded reliefs with charcoal or airbrush

Today:

• digital terrain modeling

• geovirtual reality

Methods for depicting terrain (+example)

What are the 2 approches for depicting terrain?

vertical (orthographic)

oblique (persepctive, bird’s eye)

Methods for depicting terrain:

• Vertical plane views

2D map perpendicular to the vertical datum plane

uses elements to depict terrain

• hachure

• physiographic

• contour lines

• shaded relief (hillshading)

• geomorphological representations

What is hachure?

short lines of varying width drawn in direction of steepest gradient, usually combined with lightning effect

What are contour lines?

What is equidistance?

lines that connect points of equal elevation, usually relative to mean sea level

equidistance is the Δ elevation between two neighbouring contour lines

→ show geomorphological forms

→ terrain can be imagined

What is hillshading (shaded relief)?

light source (usually from NW) is casted across terrain to create lighted and shadowed parts

How does analytical hillshading work?

raster analysis function with defaults (azimuth: 315° and altitude/illumination 45°)

1. Calculate the slope gradient (inclination) and the slope aspect (direction/azimuth)

2. Set illumination: sun azimuth and elevation

3. Estimate reflectance of the surface

4. Assign map reflectance value to RGB (colors).

Name one example for vertical views

Swiss style

• Sun tint (1)

• Relief shading (2)

• Contour lines (3)

• Rock drawing: depiction of outcrop/bedrock exposures (4)

• Scree pattern (= Geröll): depiction of loose rocks covering a slope (5)

Name a second example for vertical views

Hypsometric tinting

Use of color hues to represent terrain & enhance relief cues

• Color transition is continuous/smooth

• Low altitudes, fertile → greenish

• Medium altitudes, above tree line → brownish

• High altitudes, snow/rocks → blueish/white

Methods for depicting terrain:

• Oblique views

appear 3D, but are 2D on surfaces

• panoramas / panorama maps

• draped images

• block diagrams

What are pros and contras for oblique views?

PRO

• More attractive

• Lack of abstraction

• Digitally easy to produce

CONTRA

• Not as accurate as plane views

• Traditionally only a single view oblique was possible

• Traditionally difficult/expensive to produce

What are panorama maps?

• More picture-like representation, less abstract

• Distorted

• Popular in tourism (e.g. ski region maps)

• Production: handmade or digital (DEM)

What are draped images?

Images that are draped over the terrain with DEM

can be aerial photo / satellite image / raster map

What are block diagrams?

Oblique view of a terrain including a cutaway of the subsurface

You can also add geological features

What can be represented with topographic maps?

• Configuration of landscapes without relief

  • Urban areas (buildings)

  • Transportation network (roads)

  • Hydrography, water bodies (rivers, lakes)

  • Landcover (vegetation, cropland)

  • Individual features (antenna)

  • Boundaries (of countries) •

• Terrain (with relief, 3D)

• Toponyms (Labelling of the features)

• Map grid, marginalia

Basic functions of topographic maps

1. Show the spatial configuration of natural and manmade features (what,where)

2. Show relationship, topology and connectivity of features

3. Show distance, direction and area

4. Tool for all spatial problems

5. Orientation, navigation and route planning

What can be analyzed with a topographic map?

Navigation

• distances

• directions

Terrain features

• Texture, surface (hue, texture)

• Elevation

• Geomorphological points

• Aspects (light direction, azimuth)

• Slope (contour lines)

• Gradients (inclination, elevation with contour lines)

What determines a good map?