CHAPTER OUTLINE

I. The Nature of Maps

A. Map — a two-dimensional representation of the spatial distribution of selected phenomena.

B. Basic attributes of maps, making them indispensable:

1. Their ability to show distance, direction, size, and shape in horizontal (two-dimensional) spatial relationships.

2. They depict graphically what is where and they are often helpful in providing clues as to why such a distribution occurs.

C. Basic fault of map:

1. No map can be perfectly accurate:

a) Maps are trying to portray the impossible — taking a curved surface and drawing it on a flat piece of paper.

D. The Matter of Scale

1. Scale — gives the relationship between length measured on the map and corresponding distance on the ground. Essential for being able to measure distance, determine area, and compare sizes.

2. Scale can never be perfectly accurate, again because of the curve of Earth’s surface.

a) The smaller the area being mapped, the more accurate the scale can be.

E. Scale Types

1. Several ways to portray scale, but only three are widely used:

a) graphic scale

b) word scale

c) fractional scale

(1) Graphic scale — uses a line marked off in graduated distances; remains correct when map is reproduced in another size, because both the graphic scale line and the map size change in same dimension.

(2) Word Scale — Also called verbal scale; uses words to give the ratio of the map scale length to the distance on Earth’s surface.

(3) Fractional scale — uses a ratio or fraction, called a representative fraction, to express the comparison of map distance with ground distance on Earth’s surface.

(a) 1/63,360 is commonly used because the number in denominator equals the number of inches in one mile.

(b) Often, no units are given in a fractional scale, so the dimensions translate whether one is using inches, millimeters, or some other unit of measurement.

F. Large and Small Scale

1. The concepts of “large” and “small” are comparative, not absolute; it all depends on the frame of reference whether one considers something large or small.

2. Large-scale map — has a relatively large representative fraction, which means the denominator is “small” — 1/10,000 is large-scale as compared to 1/1,000,000.

a) Portrays only a small portion of Earth’s surface, providing considerable detail.

3. Small-scale map — has a small representation fraction, which means the denominator is “Large.”

a) Portrays a larger portion of Earth’s surface, but gives only limited detail.

II. Map Projections

A. Map projection — the system used to transform the rounded surface of Earth to a flat display.

B. The fundamental problem with mapping is how to minimize distortion while transferring data from a spherical surface to a flat piece of paper.

C. Most maps are derived by mathematical computation, not by tracing a globe’s depiction onto a paper.

D. Many ways to manipulate the data to mitigate distortion:

1. Arrange grid system so that the geometric properties of the globe are retained;

2. Have most distorted areas fall in less important parts of map;

3. Interrupt the map with blank spaces in oceanic regions to decrease distortion of continents.

a) Central meridians — meridians that pass through center of major landmasses and serve as a baseline from which continents can be mapped.

E. The Major Dilemma: Equivalence versus Conformality

1. Central problem in constructing and choosing a map projection:

a) Impossible to perfectly portray both size and shape, so must strike a compromise between equivalence and conformality.

(1) Equivalence — the property of a map projection that maintains equal areal relationships in all parts of the map.

(2) Conformality — the property of a map projection that maintains proper angular relationships of surface features.

b) Can only closely approximate both equivalence and conformality in maps of very small areas (e.g., large-scale maps).

(1) Mapmaking must be an art of compromise.

(a) Robinson projection, in figure 2–11 is one of the most popular methods for compromising between equivalence and conformality.

2. Equivalent projection -- portrays equal areal relationships throughout, avoiding misleading impressions of size.

a) Disadvantages:

(1) Difficult to achieve on small-scale maps, because they must display disfigured shapes:

(a) Greenland and Alaska usually appear squattier than they actually are on equivalent projections.

(2) Even so, most equivalent world maps are small-scale maps.

3. Conformal projection -- maintains proper angular relationships in maps so the shape stays accurate (e.g., Mercator projection).

a) Disadvantages:

(1) Impossible to depict true shapes for large areas like continents.

Biggest problem is that they must distort size (e.g., usually greatly enlarges

III. Isolines

A. Isoline — commonly used cartographic device for portraying the spatial distribution of some phenomenon. Also called isarithm, isogram, isopleth, and isometric line.

1. Refers to any line that joins points of equal value.

B. Isolines help to reveal spatial relationships that otherwise might go undetected.

1. They can significantly clarify patterns that are too large, too abstract, or too detailed for ordinary comprehension.

C. Most relevant types of isolines to this course:

1. contour line

2. isobar

3. isogonic line

4. isohyet

5. isotherm

a) Contour line — joins points of equal elevation.

b) Isobar — joins points of equal atmospheric pressure.

c) Isogonic line — joins points of equal magnetic declination.

d) Isohyet — joins points of equal quantities of precipitation.

e) Isotherm — joins points of equal temperature.

D. Basic characteristics of isolines:

1. They are always closed lines, having no ends;

2. They represent gradations in quantities, so only touch or cross one another in very rare and unusual circumstances;

E. Interval -- the numerical difference between one isoline and the next:

1. Size of interval is up to the cartographer’s discretion, but it is best to maintain a constant interval thorough a map.

2. Their proximity depends on the gradient (that is, the change in the interval).

a) The closer they lay together, the steeper the gradient; the further apart they lay, the more gentle the gradient.

IV. The Global Positioning System

A. Global Positioning System (GPS) — a satellite-based system for determining accurate positions on or near Earth’s surface. High-altitude satellites (24) continuously transmit both identification and position information that can be picked up by receivers on Earth. Clocks stored in both units help in calculating the distance between the receiver and each member of a group of four (or more) satellites, so one can then determine the three-dimensional coordinates of the receiver’s position.

1. Military units allow a position calculation within about 30 feet (10 meters).

2. Also used in earthquake prediction, ocean floor mapping, volcano monitoring, and mapping projects.

V. Geographic Information Systems

A. Geographic information systems (GIS) — automated systems for the capture, storage, retrieval, analysis, and display of spatial data.

1. Uses both computer hardware and software to analyze geographic location and handle spatial data.

2. Virtually, libraries of information that use maps instead of alphabet to organize and store data.

a) Allows data management by linking tabular data and map.

b) Mainly used in overlay analysis, where two or more layers of data are superimposed or integrated.

c) First uses were in surveying, photogrammetry, computer cartography, spatial statistics, and remote sensing; now being used in all forms of geographic analysis, and bringing a new and more complete perspective to resource management, environmental monitoring, and environmental site assessment.

d)

VI. FOCUS: Map Essentials

A. Maps should include eight essential components; omitting any of these components will decrease the clarity of the map and make it more difficult to read.

1. Eight essential components are: Title, Date, Legend, Scale, Direction, Location, Data Source, and Projection Type.

a) Title — should provide a brief summary of the map’s content or purpose and identify the area it covers.

b) Date — should indicate the time span in which the map’s data were collected.

c) Legend — should explain any symbols used in map to represent features and any quantities.

d) Scale — should provide a graphic, verbal, or fractional scale to indicate the relationship between length measured on the map and corresponding distance on the ground.

e) Direction — should show direction either through geographic grid or a north arrow.

f) Location — should have a grid system, either a geographic grid using latitude and longitude, or an alternative system that is expressed like the x and y coordinates of a graph.

g) Data Source — should indicate the data source for thematic maps.

h) Projection type — should indicate the type of projection, particularly for small-scale maps.