lecture 2

Question 1

why is it complicated to define coordinates

Answer 1

1. flat 2D maps are distorted
2. earth is not a perfect sphere
3. all measures contain some error

Question 2

what is the earths shape

Answer 2

an oblate spheriod ellipsoid

Question 3

earth –> ellipsoid

Answer 3

mathmatical representation

Question 4

ellipsoid

Answer 4

used as a reference surface for horizontal coordinates
3D reference shape based on ellipse
- polar flattening and eccentricity
- around 30 ellipsoids used

Question 5

geoid

Answer 5

earth shaped

• made from precise measurements of gravity
• vertical reference surface

Question 6

relationship of ellipsoid vs geoid

Answer 6

earths surface bulges above or depressed below ellipsoid
ellipsoid replicates approximate shape of earth (horizontal)
- geod replicates vertical structure

Question 7

ellipsoid/ geod –> datum (reference surface)

Answer 7

mathmatical empirical definition

Question 8

datum

Answer 8

use info about the size and shape of the earth (ellipsoids and geoids) with a reference point to describe the location of other points on the earth
horizontal –> ellipsoid
vertical (elevation) –> geoid

Question 9

horizontal datums

Answer 9

local - north american datum NAD

global - world geodetic system of 1984 WGS84

Question 10

vertical datums

Answer 10

origin or zero point based on geoid
mean sea level to approximate height
- global: global sea level observing system (GSLOS)
- local: US national geodetic vertical datum (NAVD88)

Question 11

datum (reference surface) –> globe

Answer 11

physical measurements

Question 12

what is a coordinate system

Answer 12

system used to register and measure horizontal and vertical locations on the Earth
- movement over x and y axis

Question 13

lat/long

Answer 13

latitude- angular distance from the equator
- going up the ladder
longitude- angular distance from prime meridian
- lengthwise

Question 14

parallels & meridians

Answer 14

parallels: lines of latitude are the same distance apart
0-90
meridians: lines of longitude are varying distances
0-180

Question 15

formats of geographic coordinates

Answer 15

decimal degrees:
ddd degree mm’ss”
minutes seconds :
123.3656

Question 16

what is a map projection

Answer 16

arrangement of the coordinates of a 3D earth onto a 2D plane
- planar, cylinder, conic

Question 17

projection properties

Answer 17

line or point on a map has to be the same scale as the reference globe

• aim to preserve geographic properties
  ex. area, angles, distances, directions, compromise

Question 18

exmaples of projections

Answer 18

albers equal area conic- maintains size
lambert conformal conic- maintain angles
lambert azimuthal equal area- maintain area
azimuthal equidistant- maintain distances
mollweide equal area- maintain area
goodes homolosine interrupted- methods of area and shape

Question 19

scale factor

Answer 19

map scale is an average scale
if no distortion: SF 1.0
if stretched: SF > 1
if compressed: SF < 1

Question 20

UTM (universal transverse mercator)

Answer 20

projected coordinate system

- easting and northing

Question 21

what do GPS coordinates depend on

Answer 21

1. how to take points on a 3D surface and translate onto 2D
2. the models we use to describe the earth (ellipsoid and geoid)
3. measurements we reference our coordinates to (datum)