Relief Portrayal

January 23, 2006Geog 258: Maps and GIS

Outlines

How relief is portrayed?1. Absolute-relief portrayal methods2. Relative-relief portrayal methods3. Combining relief portrayal methods4. Dynamic relief portrayalDigital data for relief portrayal5. DEM (Digital Elevation Model)

1. Absolute-relief methods • Provides relief in a numeric scale

– You can determine exact value of elevation or water depth at individual points from this kind of map

• Designed to give precise measurements– You can measure slope from this kind of map– You can create profile from this kind of map

• Common methods include– Contours: lines of equal elevation– Isobath: lines of equal water depth– Hypsometic tints: color-coded contour interval

Contours

• Think of contours as lines obtained by cutting terrain horizontally with imaginary planes in equal intervals

• Contours are lines of equal elevation

Types of contours• What would terrain

look like inside depression contour?

• Not all contours are labeled: index contour is labeled, shown as thick lines

What is contour interval from this map?

Isobaths

• Lines of equal water depth

Further questions:

Any difference compared to contour map?

Hypsometric tinting

• Space between contour lines is color-coded

Does this look better than a contour map? Why do you think so?

Hypsometric tint

Is color coding scheme good?

Hypsometric tint

Spectral color progression

Vignetted hypsometric tints

2. Relative-relief methods• Designed to give a general impression of relative

heights of landform rather than its exact values at individual points

• Focused on providing realistic presentation of relief

• Different ways to create 3D effect• Commonly used methods include

– Physical relief model: raised relief– Perspective view: oblique vantage point– Relief shading: imaginary light source

Physical model of relief

• Physical 3D model of relief

Raised relief globes

Relief models

Raised relief topographic map

Perspective views

• Creates 3D effect with oblique vantage points

Perspective views

Landscape drawings

Perspective views

Fishnet maps (terrain profiles) Block diagram

Relief shading

• Creates 3D effect using an imaginary light source

Shaded relief map Vertical aerial photo

3. Combining relief methods

• Absolute methods are good for making measurements, but it is hard to have a general sense of terrain variation

• Relative methods are good for gaining a general impression, but it does not give precise measurements

• Why not combine both?

Which methods are combined in this map?

Absolute RelativeContour Physical

modelIsobath Perspective

viewsHypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute Relative

Contour Physical model

Isobath Perspective views

Hypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute RelativeContour Physical

modelIsobath Perspecti

ve views

Hypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute Relative

Contour Physical model

Isobath Perspective views

Hypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute Relative

Contour Physical model

Isobath Perspective views

Hypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute Relative

Contour Physical model

Isobath Perspective views

Hypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute Relative

Contour Physical model

Isobath Perspective views

Hypsometric tinting

Relief shading

Which methods are combined in this map?

Absolute Relative

Contour Physical model

Isobath Perspective views

Hypsometric tinting

Relief shading

4. Dynamic relief portrayal• Putting relief portrayal into motion• Can gain dynamic impression of landform• Animated methods

– A sequence of maps is animated detect changes– A series of images taken from different vantage points are

combined to create animation fly-over• Interactive methods

– You can choose the location, vantage points, and so on• Demo

– http://www2.jpl.nasa.gov/srtm/– http://geology.asu.edu/~reynolds/topo_gallery/topo_gallery.htm– http://www.truflite.com/

5. Digital Elevation Model • Some maps can be made by hand

– Relief globe, hachures, block diagram• These days maps are increasingly generated by

computers– Shaded relief map, profile map, fly-over– Combining methods are easily manipulated

• Basis of computer-generated terrain mapping is Digital Elevation Model (DEM)

• DEM stores elevation or water depth in regularly sampled points

• DEM can be thought of as varying elevation values stored in matrices