Digital Elevation Models (DEM); terrain analysis and visualization

The ‘graphic calculus’:

• Question: How much is 1 + 1 = ?
• Answer: 3 or more.
• (Josef Albers)
• due to: “the endlessly contextual and interactive nature of visual elements”

Reading Corner

• Chapter 3: Questions? Discussion? ....

Reading Assignment for next week:

• Chapter 4: Getting the Map Into the Computer

Announcements:

• Repeat: There will be a lecture on Thursday March 16
  • correct it in your course outline, and/or
  • write it in your planner/scheduler
• Instructor-and-Ombudspersons Meeting: Today at 2:30

Self Study: what we won’t cover today on:

• Digital Elevation Models (DEM)
• Terrain Analysis and Visualization (“A&V”)

The Structure of the Lecture:

• Debt from last week: Logic functions
• Cartographic Visualization
• Digital Elevation Models (DEM)

Debt from last week: Logic functions

Let’s solve together:

• The Truth table for: A XOR B

Exercise

• Write down, on a piece of paper, the Truth Table for NAND

Venn Diagrams

• (* diagram/blackboard*)

Small Group Assignment

• Represent using a truth table the solution for:
• (A ^ B) v C

We can represent logic statements using

• symbolic clauses (text/equations)
• tables (TTs)
• diagrams (Venn...)
• maps — when our object terms are spatial entities

symbolic clauses can be transformed based on

• logic rules of inference, and
• rules of replacement
• [*transparency*]

Basic logic plays an important role in GIS

• where there is often a need/use/application for it

Set Overlay (logical map overlay)

Selective Set Overlay Operations

• And, Or, Not, Cross

What these Operators and Operations do:

• they check co-occurrence of sets of values on 1 layer and a constant, or, co-occurrence of sets of values on n layers.

AND, OR, and NOT are implemented as Operators

AND and OR are Boolean Operators (T/F)

Can be used for simple Logic work

Cross does set intersection (conjunction) and union (disjunction) and is implemented as an Operation.

Cross and its modifiers (note the hierarchical structure!)

• Cross mapname [And mapname...]
  • [Assigning value to range/value list

• [With range/value list...] ...]

Explanation of the operation and its modifiers:

• Note that all the assigned values can be a single value or a range/value list.
• Cross is like a multi-layer recode

Complete Set Overlay

Combine and its modifiers

Combine mapname [With mapname...]

Explanation of the operation and its modifiers.

Combine gives all the combinations.

• It is exhaustive (complete)

The new zones are numbered sequentially, hence lose their identity.

The real result of Combine is the information in the Text field of the Legend.

Comments: Combine saves work in specifying lengthy Cross operations.

• Combine is to Cross what Slice is to Recode.

Combine is great for finding errors of omission and comission.

Combine with VoidMap is a good trick:

• used for giving a regular running sequence of serial numbers to data.

More on Layer Superimposition

• Cover
  • and the Mosaic modifier
• Subscene

Transparent Overlay, Mask Overlay, Mosaic and SubScene—Cover

Cover and its modifiers:

• Cover map [With map] Mosaic

Explanation of the operation and its modifiers.

Note that [With map] can be repeated several times.

The default spatial extent of the operation, when the layers are not identical in size and/or position, is the set intersection of the space.

The Mosaic modifier is used to specify that the result map is a rectangle that is large enough to accomodate the union of the spatial extents.

This modifier enables the use of Cover for Mosaicking or Joining (areal superset expansion).

An Example.

• /* Cover Land Cover with the waterways, the buildings, and the roads */
• ViewInContext = Cover «Land Cover» With RankedWaterSheds With Buildings With Transportation ;

What would happen if Mosaic is used?

What would happen if Mosaic isn’t used but one of the maps is smaller in its areal extent?

Note: watch out, and correct, for the above problem in Ass 3.

The paired Recode and Cover (or vice versa) are a very common sequence in procedures.

• used to isolate the desired elements
• and to avoid mixing up numerical zone/category IDs

Windowing—SubScene

Creating a rectangular areal subset.

• This is the exact opposite of joining: “splitting”, reducing the size of the layer.

SubScene and its modifiers:

• SubScene map Rows range Columns range

Explanation of the operation and its modifiers.

An Example. The use of SubScene:

• /* Make the subscene for Assignment X */
• HydrologySub = SubScene Hydrology Rows 100…340 Columns
• 1260…1470 ;

Less cells per layer without changing cell resolution.

Concluding Note:

• How Spatial Are Basic Operations II?

The Question is:

• Now that I have a derived/transformed map, how do I “render” it?

Color and MFworks

The Apple HSL Color Model

• origins:
  • Munsell (beginning of 20th century)
  • Tektronix HSL (in the 70’s)

HSL models are widely used by Cartographers (examples to follow...)

• Flight of Fantasy
  • RGB Cloud..

Literature:

• Dent Borden D., (1996). Cartography: Thematic Map Design, 4th Ed., Wm. C. Brown, USA.
• Robinson, Morrison, Muehrcke, Kimerling, Guptill (1995) Elements of Cartography, John Wiley and Sons, Sixth Edition.
• Spiess E., (1988), Map Compilation,Chapter 2 (pp. 23-69), in Basic Cartography — for students and technicians, Vol. 2, R.W. Hanson, Ed., Published for the ICA by Elsevier Applied Science Publishers, London and New York.

• Brewer Cynthia A., (1994), Color Use Guidelines for Mapping and Visualization, Ch. 7 in , Visualization in Modern Cartography, MacEACHREN, Alan M. and D. Taylor, Eds., New York: Elsevier Science, Modern Cartography Series.
• Keller P. R. and M. M. Keller, 1993, Visual Cues, USA: IEEE Computer Society Press and IEEE Press, 229p.
• Murch G., (1987). Color Displays and Color Science, in Color and The Computer, H. J. Durrett, Ed., Ch. 1, pp. 1-25, Academic Press, Orlando, FLA.
• Olson Judy M., (1987). Color and the Computer in Cartography, in Color and The Computer, H. J. Durrett, Ed., Ch. 1, pp. 205-219, Academic Press, Orlando, FLA.
• Tufte E. R. (1990). Envisioning Information, Graphics Press, New Haven, CN.

MFworks Colorization — of a single layer

Single color

Color sequences — “paths”

• monochome
• linear RGB (2-color sequence)
• multichrome
• composite sequences: series or sets of sequences

Color Class Schemes: Sequential, Zone Value, Zone Area

End of Lecture