090710.doc

9/7/10 Geographic Coordinates -Geodesy -science of determining the shape of the Earth -Earth is (roughly) and ellipsoid -flattened-out sphere -centrifical force and gravity cause distorted shape -Geographic Coordinates System -system of latitude and longitude -latitude runs East/West -indicates how far North/South you are of the Equator -each line of latitude is parallel to the other lines of latitude -therefore, latitude lines can also be called ?parallels? -location in latitude is the angle of degrees between center of the Earth measuring from Equator to location -places North of Equator can have positive numbers compared to negative numbers if South (not always shown this way) -longitude runs North/South -indicates how far East/West you are from the Prime Meridian -Prime Meridian runs through Greenwich, England -arbitrary starting point -measured in angles from Prime Meridian -lines are not parallel, they converge at the poles -longitude lines are also called ?meridians? -East of Prime Meridian can be indicated in positive numbers, West can be negative numbers (not always indicated this way) -Graticule -grid of latitude and longitude -can be used to find out where things are located -irregular surface of the Earth does not exactly match the idealized ellipsoid -locations and distance are therefore an estimate, not exact -even though not exact, ellipsoid is used because it is simple -variety of ellipsoids are available through cartographic sciences -chose most accurate ellipsoid for area that is being mapped -if looking at a map, pay attention to the ellipsoid that was used to understand basis of data -the graticule grid does not give any elevation information -Geoid -model of the Earth?s gravitational pull/fields -Earth?s gravity varies across the surface of the planet -minerals and other surface components effect the gravity at a location -example: higher density components (like rock) has a higer gravitational pull -geoid can be used to estimate elevation -Datum -complete set of reference to figure out where something is on the Earth -uses ellipsoid and geoid depending on the information needed (location vs. elevation) -different countries have different datums that fit their location best -must have information about the original reference points to used software -Flat-Earth View -used when ellipsoid/geoid model is too complex for the area being mapped -useful for small areas being mapped (such as a city or neighborhood) -Projections -mapping creates problem of how to display the rounded shape on a flat (2-D) environment -distortion MUST occur in order to show the Earth as flat -projections indicate where/how that distortion is dispersed -must know the type of projection to provide evaluation of information on a map -knowing what projection was used on a map allows you to undo the projection and apply a different type