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How relief is portrayed?
1. Absolute-relief portrayal methods
2. Relative-relief portrayal methods
3. Combining relief portrayal methods
4. Dynamic relief portrayal
Digital data for relief portrayal
5. 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
Hypsometric tinting
• Space between contour lines is color-coded
Does this look better than a contour map? Why do you think so?
Vignetted* hypsometric tints
*Vignette definition: In photography and optics, vignetting is a reduction of an image's brightness or saturation at the periphery compared to the image center. en.wikipedia.org/wiki/Vignetting
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
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 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
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