Table of Contents
The Geographic Grid
A. A system of accurate location is necessary to pinpoint with mathematical precision the position of any spot on Earth’s surface.
1. The grid system is the simplest technique, using a network of intersecting lines.
2. Graticule: the grid system for mapping Earth that uses a network of parallels and meridians (lines of latitude and longitude).
3. Equator: the imaginary midline of Earth, where the plane of the equator intersects Earth’s surface. Is the parallel of 0° latitude.
4. Great Circle: the largest circle that can be drawn on a sphere; it must pass through the center of the sphere; it represents the circumference and divides surface into two equal halves or hemispheres.
5. Small circle: a plane that cuts through a sphere without passing through the center.
6. Graticule: grid system of the Earth consisting of lines of latitude and longitude.
1. Latitude: the distance measured north and south of the equator; it is an angular measurement, so is expressed in degrees, minutes, and seconds.
2. Parallel: an imaginary line that connects all points of the same latitude; because they are imaginary, they are unlimited in number.
3. Seven parallels are particularly significant.
a) Equator, 0°
b) North Pole, 90° N
c) South Pole, 90° S
d) Tropic of Cancer, 23.5° N
e) Tropic of Capricorn, 23.5° S
f) Arctic Circle, 66.5° N
g) Antarctic Circle, 66.5° S
4. Regions on Earth are sometimes described as falling within general bands of latitude.
a) Low latitude: generally between the equator and 30º N and S
b) Midlatitude: between about 30º N and S
c) High latitude: latitudes greater than about 60º N and S
d) Equatorial: within a few degrees of the equator
e) Tropical: within the tropics (between 23.5º N and 23.5º S)
f) Subtropical: slightly poleward of tropics, generally around 25–30º N and S
g) Polar: within a few degrees of the North or South Pole
5. Nautical Miles
a) The actual length of one degree of latitude varies according to where it is being measured on Earth, because of the polar flattening of Earth. Even with the variation, each degree has a north–south length of about 111 kilometers (69 miles).
b) A nautical mile is defined by the distance covered by one minute of latitude (1.15 statute miles or 1.85 kilometers).
1. Longitude: the distance measured east and west on Earth’s surface.
2. Meridian: imaginary line of longitude extending from pole to pole (aligned in a north–south direction), crossing all parallels at right angles. (It’s not to be confused with its other definition, the sun’s highest point of the day.)
3. Prime Meridian: the meridian passing through the Royal Observatory at Greenwich, England. Longitude is measured from this meridian both east and west to a maximum of 180°.
Latitude and Longitude (3:14)
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 maps: No map can be perfectly accurate. Maps are trying to portray the impossible: taking a curved surface and drawing it on a flat piece of paper.
A. Map 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.
B. Scale can never be perfectly accurate, again because of the curve of Earth’s surface. The smaller the area being mapped, the more accurate the scale can be.
C. Scale Types
1. Several ways to portray scale, but only three are widely used.
a) Graphic Map Scales: 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.
b) Fractional Map Scales
(1) Uses a ratio or fraction, called a representative fraction, to express the comparison of map distance with ground distance on Earth’s surface.
(2) 1/63,360 is commonly used because the number in denominator equals the number of inches in one mile.
(3) 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.
c) Verbal Map Scales: Also called word scale; uses words to give the ratio of the map scale length to the distance on Earth’s surface.
D. 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. 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.” Portrays a larger portion of Earth’s surface, but gives only limited detail.
Maps should include a few essential components; omitting any of these components will decrease the clarity of the map and make it more difficult to read.
Advantages of Globes
A. Can maintain the correct geometric relationships of meridian to parallel, of equator to pole, of continents to oceans.
B. Can show comparative distances, comparative sizes and accurate directions.
C. Can represent, essentially without distortion, the spatial relationships of features on Earth’s surface.
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. 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.
2. Equivalent projection: portrays equal areal relationships throughout, avoiding misleading impressions of size.
(1) Difficult to achieve on small-scale maps, because they must display disfigured shapes. 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).
(1) Impossible to depict true shapes for large areas like continents.
(2) Biggest problem is that they must distort size (e.g., usually greatly enlarges sizes in the higher latitudes.
Families of Map Projections
A. Cylindrical Projections
1. Cylindrical projections are created by mathematically “wrapping” a globe in a cylinder.
2. The paper touches, or is tangent to, the globe only along the equator. This forms a circle of tangency.
4. Mercator: The Most Famous Projection
a) The Mercator projection: a special-purpose projection that was created more than 400 years ago as a tool for straight-line navigation.
b) Prime advantage: shows loxodromes as straight lights.
Loxodrome: also called rhumb line, is a curve on the surface of a sphere that crosses all meridians at the same angle. They approximate the arcs of a great circle but consist of constant compass headings.
c) How do navigators use Mercator projection?
(1) First, navigators must use another type of projection that shows great circles as straight lines; they draw a straight line between their starting point and destination.
(2) They then transfer that straight-line route to a Mercator projection by marking spots on the meridians where the straight-line route crossed them.
(3) They then draw straight lines between the meridian points, which are loxodromes or rhumb lines.
(4) The navigator can use these loxodromes to chart when periodic changes in compass course are necessary to approximate the shortest distance between two points.
d) Why does the Mercator projection distort size?
(1) It is a conformal projection. Although it is accurate in its portrayal of the equator and relatively undistorted in the low latitudes, it must distort size in the middle and high latitudes in order to maintain conformality, that is, approximate the shapes of landmasses.
(2) It shows the meridians as straight, parallel lines instead of having them converge at the poles as they actually do. This causes east–west stretching. To compensate for this stretching and keep shapes intact, the Mercator projection must also stretch north–south, so it increases the spacing between parallels of latitude as one goes further from the equator. Thus landmasses further away from the equator appear larger than they actually are.
e) The Mercator projection has been misused and so creates many misconceptions about the size of landmasses, as it makes those landmasses in the high latitudes appear much larger than they actually are.
(2) Indeed, Africa is 14 times larger than Greenland.
B. Planar Projections
1. Planar projections (AKA azimuthal projections or zenithal projections) are created by projecting the markings of a center-lit globe on a flat piece of paper.
2. There is only a point of tangency that is usually located on one of the poles, and distortion increases as distance increases from this point.
3. The disadvantage of this projection is that no more than one hemisphere can be displayed.
C. Conic Projections
1. A conic projection is created by projecting the markings of a center-lit globe onto a cone wrapped tangent to, or intersecting, a portion of the globe.
3. Distortion increases with distance from this circle. As such, conic projections are best used with landmasses possessing great east–west orientations.
4. Because of the distortion associated with them, they are better suited for mapping smaller regions (i.e., a single country).
D. Pseudocylindrical Projections
1. Pseudocylindrical projections (AKA elliptical projections of oval projections) are generally designed to show the entire globe.
2. These projections usually employ a central parallel and a central meridian that cross at right angles in the middle of the map.
3. Distortion usually increases in all directions away from the point where these lines cross.
1. The interruption of a projection is a technique used to minimize distortion.
2. Ocean regions are usually split apart or “interrupted” so that the distortion over landmasses is minimized.
3. The result is a map with very little distortion over land and great “gaps” over the oceans.
Review the material at Ball State’s Map Projections Tutorial. You might also try the University of Colorado at Boulder’s Map Projections Overview. Then jump over to A Multitude of Maps for some interactive map and projection work. (There are 8 steps. They’re linked at the bottom of each section.) These sites should provide you with enough working knowledge of map projection differences. [FYI: The National Map]
Computer technology has provided several great benefits to cartography.
A. Improved speed and data-handling ability
B. Reduced time involved in map production
C. Ability for cartographer to examine alternative map layouts
A. Isoline: commonly used cartographic device for portraying the spatial distribution of some phenomenon. Also called isarithm, isogram, isopleth, and isometric line. Refers to any line that joins points of equal value.
B. Isolines help to reveal spatial relationships that otherwise might go undetected. 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. Elevation contour line: joins points of equal elevation
2. Isotherm: joins points of equal temperature
3. Isobar: joins points of equal atmospheric pressure
4. Isohyet: joins points of equal quantities of precipitation
5. Isogonic line: joins points of equal magnetic declination
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.
3. Interval: the numerical difference between one isoline and the next; Size of interval is up to the cartographer’s discretion, but it is best to maintain a constant interval thorough a map.
4. Their proximity depends on the gradient (that is, the change in the interval). The closer they lie together, the steeper the gradient; the further apart they lie, the more gentle the gradient.
The Global Positioning System (GPS)
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.
A. Military units allow a position calculation within about 30 feet (10 meters).
B. Also used in earthquake prediction, ocean floor mapping, volcano monitoring, and mapping projects.
C. Because of accuracy of GPS units, latitude and longitude are increasingly being reported in decimal form.
A. Remote sensing: study of an object or surface from a distance by using various instruments.
1. Sophisticated technology now provides remarkable set of tools to study Earth, through precision recording instruments operating from high-altitude vantage points.
2. Different kinds of remote sensing: Aerial photographs, color and color infrared sensing, thermal infrared sensing, microwave sensing, radar, sonar, multispectral, and SPOT imagery.
B. Aerial Photographs
1. First form of remote sensing
2. Aerial photograph: photograph taken from an elevated “platform” such as a balloon, airplane, rocket, or satellite
a) Either oblique or vertical
(1) Oblique: camera angle is less than 90°, showing features from a relatively familiar point of view.
(2) Vertical: camera angle is approximately perpendicular to Earth surface (allows for easier measurement than oblique photographs).
b) Photogrammetry: science of obtaining reliable measurements from photographs and, by extension, the science of mapping from aerial photographs.
C. Orthophoto Maps
Orthophoto maps: multi-colored, distortion-free photographic maps produced from computerized rectification of aerial imagery.
1. Show the landscape in much greater detail than a conventional map, but are like a map in that they provide a common scale that allows precise measurement of distances.
2. Particularly useful in flat-lying coastal areas because they can show subtle topographic detail.
D. Color and Color Infrared Sensing
1. Color: refers to the visible-light region of the electromagnetic spectrum.
2. Color infrared (color IR): refers to the infrared region of the spectrum.
a) Color IR film is more versatile; uses include evaluating health of crops and trees.
b) Color IR film cannot detect much of the usable portion of the near infrared. Scanner systems have come to aid, by being able to sense much further into infrared.
c) Landsat: a series of satellites that orbit Earth and can digitally image all parts of the planet except the polar regions every nine days.
E. Thermal Infrared Sensing
1. Thermal Infrared Sensing (thermal IR): middle or far infrared part of electromagnetic spectrum; can’t be sensed with film.
2. Thermal scanning is used for showing diurnal temperature differences between land and water and between bedrock and alluvium, for studying thermal water pollution, for detecting forest fires, and, its greatest use, for weather forecasting.
F. Microwave Sensing
Microwave radiometry: senses radiation in the 100-micrometer to 1-meter range. Useful for showing subsurface characteristics such as moisture.
G. Multispectral Remote Sensing
1. These systems image more than one region of the electromagnetic spectrum simultaneously from the same location.
a) The early Landsat was the multispectral scanning system (MSS): a system that images Earth’s surface in several spectrum regions.
b) Landsat Sensory Systems use an MSS; can gather more than 30 million pieces of data for one image 183-by-170 kilometers (115-by-106 miles).
3. Thematic mapper: uses seven bands to improve resolution and greater imaging flexibility. Images in eight spectral bands with a resolution of 15 meters became available with the launching of Landsat 7 in 1977.
4. In 1999, Landsat 7 was launched, carrying an enhanced thematic mapper plus (ETM+) It uses eight spectral bandwidths with a resolution of 15 meters in the panchronic band, 30 meters in the visible and infrared network, and 60 meters in the thermal infrared.
H. Earth Observing System Satellites
1. NASA’s Earth Observing System (EOS) satellite Terra was launched in 1999.
2. The satellite contains a moderate resolution imagery spectroradiometer (MODIS) that gathers 36 spectral bands.
3. The latest device is a multiangle image spectroradiometer (MIS) that is capable of distinguishing various types of atmospheric particulates, land surfaces and cloud forms.
4. The most recent EOS satellite Aqua monitors water vapor, precipitation, clouds, glaciers, and soil wetness. Aqua also includes the atmospheric Infrared Sounder (AIRS), which permits accurate atmospheric temperature measurements.
I. Radar and Sonar Sensing
1. Radar: (radio detection and ranging) senses wavelengths longer than 1 millimeter and now provides images in photo-like form.
2. Sonar: (sound navigation ranging) permits underwater imaging.
A. Uses both computer hardware and software to analyze geographic location and handle spatial data.
B. Virtually, libraries of information that use maps instead of alphabet to organize and store data.
1) Allows data management by linking tabular data and map.
3) 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.
4) GIS was also used to compile structural data on the rubble at Ground Zero at the World Trade Center disaster. The technology allowed the building damage to be mapped and provided details on the outage of various utilities in the area.
Global Summary: Maps and Charts