Class notes 5 - G302 Review of Maps Topographic Maps I...

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1 G302 – Review of Maps / Topographic Maps I. Introduction A. Map- a 2-d, scaled representation of the earth's surface, 1. Model of Earth's Surface 2. Basic functions: to represent horizontal distance, direction, size, and shape, as well as distributions of phenomena. B. "No map is perfectly accurate" - inaccuracy of a map is ubiquitous because it projects a curved surface on a flat piece of paper. C. Map Components 1. Title / Type of Map a. Road Map, Geologic Map, Topographic Map, Hydrologic Map, etc. b. Location of Map Coverage 2. Compilation Date (When was the map made?) 3. Legend / Explanation of Map Symbols 4. North Arrow / Geographic Frame of Reference a. Georeference (1) e.g. Longitude and Latitude b. Geographic Directions: North, South, East, West 5. Map Scale a. Mathematical Relationship Between Map Distance of Model and Actual Ground Distance II. Methods of Earth Representation A. Globes or spherical models: 1. provides the most accurate portrayal of the sphericity of the earth, but is limited in its use. (size must be at small scale, and not functional for transport, plus does not provide regional detail). B. Digital Computer Models 1. Geographic Information Systems 2. Digital Maps C. 2-D Paper Maps (Traditional) D. Map Projections 1. Problem: projecting a 3-D sphere on a 2-D surface a. All Maps Have Inherent Error in Representation b. The Larger the Area of Coverage: the greater the spatial error 2. Modeling Approaches a. Accurate Scaled Areas vs. Accurate Geometric Shapes
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2 b. Equivalence vs. Conformality (1) Equivalence: Map Projection Preserves Scaled Relationships Between Areas (a) e.g. Continental Land Areas (b) Created at the Expense of Shape Accuracy (2) Conformality: Map Projection Preserves Scaled Relationships Between Map Shapes (a) Created at the Expense of Areal Accuracy 3. Example Map Projections (100's of ways to project a 3-D sphere onto a 2-D surface) a. Cylindrical Projection b. Conical Projection III. Georeferencing System - (Grid Location Coordinates) A. Grid Location Network 1. Standard Grid a. East-West Lines (Horizontal) b. North-South Line (Vertical) 2. Frame of Reference a. Rotational axis- a diameter line that passes through the center of the Earth, about which the Earth rotates or spins about. (1) North Pole rotational axis- point of intersection of rotational axis at the upward portion or top side of the Earth (2) South Pole rotational axis- point of intersection of rotational axis at the downward portion or bottom side of the Earth b. Plane of the equator - an imaginary plane that passes through the Earth halfway between the poles and perpendicular to the axis of rotation (1) Equator- imaginary line of intersection formed between the surface of the Earth and the plane of the equator.
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