a special line on the earth that intersects every meridian at the same angle o All parallels are loxodromes because they intersect meridians at the right angles o A loxodrome is a great circle only if it is meridian/equator
Principal geometrical and mathematical relationships of the earth coordinate grid: area o 1. Meridians and parallels intersect at right angles o 2. Quadrilaterals that are formed between any two parallels and that have equal longitudinal extent have equal areas o The area of quadrilaterals between any two meridians and between similarly spaced parallels decrease poleward and increase equatorward. Geographic coordinate system o Advantages: Single system that “fits” the entire globe without any interruptions Most accurate for positions for large study areas o Disadvantages: Measure ANGLES not distances, not easy or precise to derive lengths, areas, or volumes for GIS measurements Length of one degree is not constant at all locations Geographic coordinate system o Systems of Specification: Geographic coordinates are specified in two manners, one used mainly on maps, and the other by computers: Degrees: Minutes: Seconds (D:M:S) are used on maps and reflect the geometric system of angular measurements. Used N, S, E, W designators Decimal Degrees are commonly used in computing as they are easier to deal with They are easy to convert back and forth SEE LECTURE 6 SLIDE 18 ON HOW TO CONVERT Cartesian Coordinate System: o Cartesian systems are based on two right angled axes on a plane: “origin” is the starting point. This point is usually an arbitrary location to the southwest of the area to be mapped Coordinates measure the distance of a point from the origin parallel to the axes in 2 dimensions Cartesian Coordinate System o Advantages: Measure location in units of distance rather than in angles Distance, area, and volume measurements are very straightforward and simple in GIS when using a Cartesian system o Disadvantages: Do not fit the sphere or ellipsoid models of earth. Cartesian grids are only possible on a plane (“Flat Earth”) view. This causes locational error and requires careful choice of map projection to accommodate desired Earth qualities.
- Fall '18
- Geodesy, Geographic coordinate system, Earth Coordinate Geometry