Maps: Lecture Exam 1
The size and shape of the earth; How people have calculated the circumference - determination and concept of the oblate ellipsoid.
-Rotation of the earth around the polar axis introduces outward centrifugal forces perpendicular to the axis. -The amount of force varies from zero at each pole, to a maximum at the equator.
How are map projection types grouped? Based on distortion and the map projection surface.
1. A grouping based on distortion. 2. A grouping based on the projection surface.
The shape of the earth, and how people came to the conclusion that it is spherical.
Aristotle believed the earth was spherical based on astronomical (stars and lunar eclipse) and sailing ship observations.
What are the benefits and drawbacks of both bar scales and verbal scales?
Benefit- If the map is reduced or enlarged during photocopying, the scale bar size also changes in direct proportion to the physical size of the map. Drawback - Not 100% accurate. Verbal Scales benefits - Expresses large RF denominators in more familiar units of measurement. Verbal scales drawback - Not accurate.
The effects that the projection process has on completeness
Completeness Refers to the ability of a map to show the entire earth.
Other aspects of the NPLSS: Correction lines; when states meet; inaccuracies.
Correction lines were established at every fourth township, or every 24 miles. When states meet, inaccuracies occur that need to be connected and rushed work.
Grand canyon Arizona
Dark close lines mean steep inclines
Death valley ca
Death Valley, CA 282 feet below sea level
Geocentric vs. geodetic latitude and longitude.
Geocentric latitude - the latitude (the north-south angular distance) defined by parallels on a sphere. Geodetic latitude - the angle between the equator and a line perpendicular to the ellipsoidal surface at the parallel of interest.
understand latitude and longitude
Latitude - the north-south angular distance from the equator to the place of interest. Longitude - the angle, measured along the equator, between the intersection of the reference meridian (prime meridian) and the point where the feature of interest intersects the equator.
Lehmann system / partial hachure
Lehmann- Each hachure line lies in the direction of the steepest slope, showing the amount of slope. - The steeper the slope, the shorter and wider the hachures. - A poor choice for small-scale maps: mountain ranges become "hairy caterpillars". Partial hachure- Hachures are eliminated on the north-west sides of hills on north-oriented maps.
-The effects that the projection process has on map scale, completeness, corresponding relations, and continuity.
Map Scale: Stretching occurs during a projection. Therefore, the stated scale is true only at points and lines of tangency. Point or line of tangency - The point or line "...at which the projection surface is in contact with the spherical or ellipsoidal generating globe."
Cartesian coordinates and their application to cartography. The concept of Eastings and Northings.
Map makers only use Quadrant I so that all coordinates are positive. Eastings- An easting is the distance east from the origin (0,0). Add an arbitrary value to all eastings so that none are negative, and each easting becomes a "false easting" Northings- A NORTHING is the north-south Y-coordinate in a grid coordinate system
What is map scale, and what ways may it be portrayed?
Map scale- The distance on the map represents this distance on the earth's surface. Scale may be presented in three ways: 1. Using a representative fraction (RF). 1:24,000 2. A scale bar. 3. A verbal scale.
Hachure
Maps made completely out of hachure marks
Platted lots - what are they and how are they used?
Parcels in a subdivision are specified by lot numbers.
Define navigation map
Road maps, transit maps, navigation charts.
Block diagrams
Shows a piece of the earth (top and sides), as if it had been cut out of the earth's surface.
Relative relief mapping
Shows landform features and their relative heights.
Sawyer AFB plat map
Smallest unit of land that was "forgotten" by map partitioners.
Mt washington
Summit of Mt. Washington, NH - summit elevation - 6,288 ft - highest wind gust directly measured at the Earth's surface, 231 mph,
Know some common planar, cylindrical, and conical projections.
The 3 developable surfaces. -planar / azimuthal -cylindrical -conical. Planar/azimuthal: True perspective planar projections - projected onto a plane tangent to the generating globe at a single point of tangency. Cylindrical: "...projecting onto a cylinder that touches the generating globe along any small circle or slices through the generating globe." Conical: "...projecting onto a cone with the line of tangency on the generating globe along any small circle or a cone that slices through the generating globe." Common Planar projections: Orthographic - How earth would appear if viewed from a distant planet. Common Cylindrical projections: Equirectangular - Nearly 2,000 years old. - Equally spaced parallels. - Often used for world maps. - Simple, flat map. Common Conical projections: Lambert conformal - A secant projection with two standard parallels set to minimize distortion.
What does an RF tell you?
The RF expresses the ratio between map distance and ground distance.
The effects that the projection process has on corresponding relations
The ability of a map to show a point on the earth as a corresponding point on the map. Some map projections are unable to do this for all points
Understand the idea of a geometrical reference framework (such as cardinal directions) that we use to locate places, and that we use Euclidean geometry in this process.
The four basic directions. North, West, South, East. A line connecting two or more points. Intersecting lines. Angles. Parallel and perpendicular lines. A plane- a two dimensional space that extends infinintly in all directions.
What makes maps so popular to use? (Convenience, simplification, credibility, strong visual impact.)
The language of maps is universal. Colors, symbols are easily recognizable and known.
The graticule: Understand parallels and meridians;
The network of parallels and meridians is now called the graticule. Parallels (lines of latitude) - Equally spaced eastwest lines parallel to the equator. Meridians (lines of longitude) - Imaginary northsouth lines that form half of a great circle (measuring 20,003.93 km (12,429.9 miles) on the Earth's surface with ends at each pole. Meridians are perpendicular to each circle of latitude.
Why does the earth have a different radius of curvature at the poles vs. at the equator?
The poles have a larger radius of curvature, and the equator has a smaller radius curvature of the earth.
arbitrary prime meridian (0o longitude)
The prime meridian (the point where the meridian is zero degrees) is arbitrary.
the Tropic of Cancer (23.5o N lat) and the Tropic of Capricorn (23.5oS lat).
The tropics of Cancer (north) and Capricorn (south) mark the northernmost and southernmost positions on the earth where the sun is directly overhead on the summer and winter solstices.
What is a variable scale bar, and in what situation(s) may it be used?
Variable scale bar- angles are preserved, therefore maintaining the correct shape. The requirements dictate that the variable scale bar may only be used on the Mercator projection.
Large scale vs small scale map
When considering a Representative Fraction (RF), as the denominator becomes smaller, the closer the map is to a 1:1 ratio, and therefore, the largerthe scale.
the significance of the equator (0o latitude)
a point to measure angular distance from.
Bump mapping
forest texture added to a relief shaded map.
Define aeronautical map
maps designed for the air navigator. Includes safe elevations.
Land partitioning - what is it and why is it important?
the dividing of property into parcels, also called tracts, which are areas with some implication for landownership or land use.
Relief shading
Drawings of 3-D objects appear correct when illuminated by an imaginary light source in the upper-left corner of the illustration.
What is a map projection and why do we need map projections?
"A map projection is a geometrical transformation of the earth's spherical or ellipsoidal surface onto a flat map surface." To put the earth on a tangible piece of paper to see the whole earth on a flat surface, with geometrical distortion.
The authalic sphere - what is it and why is it important?
When determining latitude and longitude with small-scale maps (maps that cover extremely large areas) the differences between locations on the sphere and the ellipsoid are negligible, and map makers use a value of the earth's spherical circumference of an authalic (area-preserving) sphere.
Government lots - what are they and how are they used?
When most of a small parcel (<10 acres) borders a body of water, then the lot will be subdivided using a government lot. So that each lot will be touching water.
Vertical exaggeration
When the vertical scale is larger than the horizontal scale. Vertical exaggeration = horizontal scale (H)/vertical scale (V)
Define thematic map
a map that focuses on a specific subject such that the subject stands out from the geographical setting.
Define reference map
a reference library of geographic information. These are the earliest types of maps known. All features are given equal prominence.
Oblique perspective and regional perspective maps
"Drape" relief shading, contours, or other map symbols over an oblique perspective fishnet map to create a perspective view regional map.
The effects that the projection process has on continuity
"To represent an entire spherical surface on a plane, the continuous spherical surface must be interrupted at some point or along some line. These breaks in continuity form the map border on a world projection."
Define persuasive map
- The mapmaker deliberately tries to persuade you to choose a certain product or support a cause. Excessive distortion of data may lead to a propaganda map.
How has land been partitioned historically?
1) Metes and bounds - was based on people choosing land that best suited their needs, no matter how irregularly shaped the resulting parcel. 2) French long lots- The seigneury was divided into narrow "long lots" (also called arpent sections), to be used for farming. 3) Land grant- Land grant - A situation where title to an area of land was given to the owner prior to that territory becoming part of the U.S. 4) The land is dissected by 6 mile by 6 mile grids. - These grid lines mark the Township and Range lines. - Each T & R grid is further dissected by a grid consisting of 36 Sections, each Section being 1 mile by 1 mile. - Each Section is quartered; each quarter is again quartered; and again each 1/16th is again quartered.
-A basic understand of the projection process
1. Define topography as elevations above, or sea depths below, the geoid. 2. Project the slightly undulating geoid onto the oblate ellipsoid surface. "Flattening" the earth. 3. Then project the ellipsoidal surface onto a plane.
What are the five characteristics that give a graphic representation of the environment its "mapness"?
1. Maps show a vertical or oblique view of the environment. 2. Maps are created at a uniform, reduced scale. 3. Made on a projection surface - a mathematically defined transformation of locations on the spherical Earth to a flat map surface. 4. Maps are a generalized representation of the environment. 5. Maps are symbolized representations of the environment.
Raised relief maps
1. Print a topographic map onto a sheet of plastic. 2. Use heat to vacuum-form it into a 3-D model of the landscape.
-Three main aspects of map use: read, analyze, interpret.
1. Reading the map - Use legends and understand what is depicted. 2. Analyzing the map - Look for patterns, take measurements. 3. Interpreting the map - How do you explain patterns or relations?
MT. hood, OR
50 miles east of Portland, OR elevation: 11,249 ft; highest point in OR
Digital Elevation Models (DEM)
A database containing sample elevations (or depths) taken on a regular grid.
The datum: What is it? Vertical and horizontal datums.
A datum is a fixed or assumed point, line or surface; a very accurate control point of known accuracy. Horizontal datum - A control point monument determined to be the exact location of a point of interest. Horizontal datum - A control point monument determined to be the exact location of a point of interest.
What is cartography?
A graphic representation of the environment
-What is a map?
A map is a model of a portion of the Earth, theme, or idea.
Relief models
A physical model of a portion of a giant globe, often showing curvature of the earth.
Karst, Lebanon, VA
An example of a karst landscape. Karst is marked by topographic depressions caused by dissolution of the underlying limestone bedrock....
-Global and local geoid - what is it?
Global geoid - a slightly undulating, nearly ellipsoidal surface that represents a surface having the same strength of gravity as mean sea level. The global geoid is determined using average mean sea level measurements for all the oceans. A local geoid (for a nation or continent) may vary from the global geoid because it is calculated using mean sea level measurements from only one or more local locations.
The concept of a mathematically developable surface; what are the developable surfaces?
The surface of a sphere is not a mathematically developable surface, meaning that it may not be flattened onto a plane without geometrical distortion. The only developable surfaces are cylinders, cones and planes.
What is topographic relief?
The vertical difference in elevation between the summits and the lowlands of a given region
Absolute mapping -
This method provides precise elevation information.
Three types of coordinate systems: a. Universal transverse Mercator (UTM) & Universal polar sterographic (UPS) b. State Plane Coordinates (SPC) c. U.S. State grids Understand how and why these systems were developed, how the coordinate systems are set up, and what type of use they are best suited for.
UTM- The Universal transverse Mercator system is world-wide. Has its own central meridian. Each UTM has a fale origin located 500,000 m west of the central meridian. This means central meridian is 500,000 m east of a false origin (0,0). UPS system- Each zone covers a circular region surrounding either the north or south pole. State Plane Coordinates- Created in the 1930's by surveyors to simplify computation of land parcel perimeters and area. This level of accuracy was achieved by covering the U.S. with multiple grids laid over map projection surfaces (versus only one grid for the entire U.S.). SPC is still very useful for: 1. Map analysis (direction and distance problems). 2. GPS applications U.S. State grids- -Zone boundaries follow state and county boundaries. -Lambert conformal projections are used for states with east-west extents. -Mercator projections are used for states with north-south extents.
-Why is latitude and longitude not always the best, or easiest system to use to determine coordinates?
because you have to take a globe, and project it onto a flat surface which causes distortion. idk.
