Chapter 2
Verbal map scale
states in word the relationship between the distance on the map and the actual distance on earth surface - EXP: one centimeter to ten kilometers
Map essentials
1) title: a brief summary of the map's content or purpose 2) Date: the time span over which information was collected, the date of publication, or both 3) Legend: An explanation of the symbol, color, and shading used to represent features on data 4) Scale: A graphic, fractional, or verbal scale 5) Direction: shown by the grid of parallels and meridians and/or a straight arrow pointing toward the north geographic poles 6) Location: latitude and longitude, x/y coordinate grid (some display more than one coordinate system) 7) Data source: The reference source that published the data 8) Projection Type: the name of the projection
Map projection
a system in which the spherical surface of earth is transformed for display on a flat surface. - mathematically transferring the features of the sphere onto a flat surface - no matter how a map projection is made, data from global (parallels, meridians, continental boundaries) cannot be transferred to a map without distortion of shape, relative areas, distance, and/or direction
Globe
a true representation of earth. Shows the spatial relationships of Earth's surface, maintaining correct size, shape, distance, and direction relationship of features around the planet.
Equivalence map projection (Map properties)
also known as Equal area map projection - the correct size ration of area on the map to the corresponding actual areas on earth's surface is maintained over the entire map. - difficult to achieve on a small scale map because correct shape must be sacrificed to maintain proper area relationships. - most shows distorted shapes of land masses especially in high latitude
Pseudocylindrical projection
- Elliptical or oval projection - a football shape map of the entire world - sometimes only the central section is used for maps of lesser areas. - wraps around the equator like an ordinary cylindrical projection but further curve in toward the poles - central parallel (the equator) and central meridian (prime meridian) cross a right angle on the middle map which is the point if no distortion
Continuously Operating GPS Reference Stations (CORS)
- Managed by The National Oceanic and Atmospheric Administration (NOAA) - Highly accurate units can detect location differences of less than 1cm of longitude, latitude, and elevation
Remote sensing
- Refers to any measurement or acquisition of information by recording device that is not in physical contact with the object understudy (exp: earth's surface)
Isolines (characteristic)
- always close lines, have no ends, often extend beyond the edge of a map. - Represent gradations in a quantity, isolines cannot touch or cross one another - the numerical difference between one isoline and the next is call "interval" (interval can vary according to the wished of the mapmaker, it is useful to maintain a constance interval all over a map) - Isolines close together indicate a steep gradient (rapid change); isolines far apart indicate a gentle gradient
Wide Area Augmentation System (WAAS)
- developed by the federal aviation administration (FAA) to increase the accuracy of instrument-based flight approach for air plain - Monitor GPS signals and then transmit correction messages to satellites - with WAAS, GPS unites achieve a position accuracy of 7 meters (95% of the time)
Isolines (drawing)
- estimate value that are not available - each dot represent a data collection location and the number next to each dot is the elevation above sea level in meters -Isoline map can reveal spatial relationship that might otherwise goes undetected
GPS (Global positioning System)
- formally called NAVSTAR GPS (Navigational Signal Timing and Ranging Global Positioning System) - Based on a constellation of at least 24 high-altitude satellites configured so that minimum of 4 (preferably 6) are in view of any position on earth
Interrupted projection
- interrupted homolosine equal-area projection - the shapes continental coastline re very well maintained even at high latitude - interrupted "torn apart" in the Pacific, Atlantic, and Indian Ocean with central meridian that pass through each major landmass; with no land area far from a central meridian
Mercator projection
- the most famous of all map projection - designed in 1569, is still commonly in use today - conformal map projection designed to navigate ocean navigation - The mercator map shows "loxodromes" as straight line - a navigator first plots the shortest distance between origin and destination on a map projection in which great circles are shown as straight line (gnomonic projection) - undistorted at the low latitudes, size distortion increase rapidly in the mid and high latitude
Isobar (Kind of Isolines)
A line joining point of equal atmosphere pressure
Conformality (Map properties)
Conformal map projection - Proper angular relationship are maintained across the entire map. - impossible to depict true shapes of large areas - For small areas, the conformal map shows correct shapes - Meridians and parallels crossing each other at right angles, just as they do on a globe - size of an area are often distorted to maintain the proper shape
Digital Elevation Models (Portraying the Three-Dimensional Landscape)
DEMs - convey topography - starting point for creating EDM image is detailed databased of precise elevations - The great virtues of DEM is that the parameter of the image, such as orientation, scale, and vertical exaggeration of the topography can be readily manipulated - Various kind of information or images can be overlain on the topography to create maps that were once impossible to conceive
GPS Application
Everything that move can be equipped with a GPS receiver. - sued in earthquake forecasting, ocean floor mapping, volcano monitoring and mapping projects _ GPS-enabled mobile devices allow ordinary people to become data collector (Crowdsourcing) -GPS units achieve greater accuracy than a regular Longitude and latitude coordinate
Map Distortions
No map can be perfectly accurate because it is impossible to portray the curved surface of Earth on a flat map without distortion. - How much of earth is being shown on the map (these distortion are always significant on a world map) - The scale on the map
Cylindrical Projections
Obtain by wrapping the globe with a cylinder paper in such a way that the paper touches the globe at the globe's equator. - the paper is "tangent" to the equator - called the "circle of tangency" - Becomes the "standard parallel" of the projection
Global Navigation Satellite System (GNSS)
Provide precise location data for points on or near Earth's surface. - System of satellite technologies included in the United State's Global positioning System (GPS) and Russian's Global Navigation Satellite System (GLONASS)
Map scale
The scale of a map describes the relationship between distance measured on the map and the actual distance it represents on Earth's surface. - Scale can never be perfectly correct over an entire map -
GPS Modernization Program
The upgrade includes replacing older satellites with newer ones (provide greater accuracy and a forth civilian broadcast L1C that is compatible with GNSS of other countries)
Map
a flat representation of the earth, shown reduce in size with only selected features or data showing. - Portray distance, direction, size, and shape in their horizontal (two dimensional) spatial relationship.
Isohyet (Kind of Isolines)
a line joining point of equal quantities of perception
Isotherm (Kind of Isolines)
a line joining point of equal temperature
Elevation contour line (Kind of Isolines)
a line joining points of equal elevation
Isogonic line (Kind of Isolines)
a line joining points of equal magnetic declination
loxodromes
a line on the surface of a sphere that crosses all meridians at the same angle as represent a line of constance compass direction - also known as rhumb line
Fractional map scales
conveys the relationship between distance measured on the map and the actual distance that represent on earth with a fraction ratio (representative fraction). - EXP: 1/250,000 = 1cm on the map is 250,000cm in the earth surface
Thematic map
design to show street patterns, the distribution of Tasmanians, the ration of sunshine to clouds, the number of earth worms/ cubic meter of soil
Small scale map (Large scale and small scale map)
has a small representative fraction - with large denominator - useful for showing geographical relationships over large area but in limited details
Large scale map (Large scale and small scale map)
has relatively large representative fraction - Use to show small portion of earth in detail - denominator is small - 1/10,000 is a larger map scale than 1/1,000,000
Compromises projections (Map properties)
it is neither equivalent nor conformal, but instead balances reasonably accurate shapes with reasonably accurate size
Conic projection
obtain by projecting the making of a center-lit globe onto a cone wrapped tangent to, or intersecting, a portion of the globe. - the apex of the cone is positioned above a pole - the circle of tangency coincides with a parallel distortion is least near this standard parallel a
Planar projection
obtained by projecting the markings of a center-lit globe on a flat piece of paper that is tangent to the globe at one point (north or south pole or some spot in the equator) - Distortion increase away from this point - show only one hemisphere
Isolines
technique for portraying the geographic phenomenon - any line that joins points of equal value of something
Elevation Contours (Portraying the Three-Dimensional Landscape)
topographic maps using elevation contour lines were a workhorse of landform study
Graphic Map scale
use a line mark off in distance to represent actual distance on earth surface - we measure the distance between any two points on the map and then compare that measures distance with the geographic map scale = direct reading of the actual distance - quickly estimate travel distance on a road map with geographic scale