CARTOGRAPHY GEODASY AND MAPPING PRINCIPALS
I. Introduction to Maps
A. Types of Maps – thematic and reference
B. Geodesy – the shape and size of Earth
1. Shape
a. sphere
b. ellipsoid
c. geoidal surface
2. Size – Eratosthenes
C. Locations as lines of Earth’s surface
1. Poles of rotation
2. Great surfaces
3. meridians – longitude
4. equator
5. small circles – latitude or parallels
6. the graticule
D. Properties of these lines on a spherical Earth
1. Parallels
a. except for the equator, all are small circles
b. true East West lines
c. equally spaced between the equator and poles
d. always the same distance apart
2. Meridians
a. halves of great circles stretching from pole to pole
b. equal length
c. true North South lines
d. spaced furthest apart at the equator and all meet at the poles
3. Parallels and meridians always cross at right angles
4. An infinite number of parallels and meridians can be drawn
E. Linear and angular distances
1. The length in degrees of latitude and longitude vary from place to place
2. the way they vary differ between latitude and longitude
3. If Earth were a perfect sphere:
a. the distance between any equi-angle pair of latitudes would be
equal
b. but because there is continuous change in Earth’s radius between
the equator and the poles, this is not quite true
c. the distance between any two meridians is never the same,
varying from 0 NM at the poles to 60.1NM at the equator
II. Projections – a rendering on a flat surface of geographic coordinates on Earth’s surface
A. Projection surfaces
1. Plane
2. Cone
3. Cylinder
B. “light source” location
1. Gnomic
2. Stereographic
3. Orthographic
C. Orientation
1. Azimuthal
2. Other tangents
3. Intersecting
D. Types of projections
1. Cylindrical
a. central
b. Mercator
c. cylindrical equal area
d. equi-rectangular cylindric
e. Gall’s stereographic
d. Miller’s cylindrical
f. transverse Mercator
2. Conic projections
a. central conic
b. simple conic
c. Lapert conformal conic
d. Alber’s equal area conic
3. Polyconic
4. Azimuthal
5. Others
a. sinusoidal
b. homolographic
c. homolosine
d. Eckert IV
e. Robinson
III Determining Latitude and Longitude
A. Latitude
1. Polaris – the angle between Polaris and the horizon = latitude
2. Sun – at equinox at LAN 90o – Sun’s altitude = latitude
B. Longitude = time
1. The astronomic longitude is the angle between the plane of a reference
meridian and the plane of the meridian of the point in question
2. Solar day
a. the time from one LAN to the next - ~24 hours later
b. divided into 24 equal parts
i. 24 hours = 360o rotation
ii. 1 hour = 15o of rotation
iii. 1 minute = 0.25o of rotation
C. Distance
1. At the equator 1o longitude = 11.32 Km. 69.17 mi, 60.11 NM
2. 1 hour = 15o
3. 1 sec = 0.004167o, 0.464 Km, 0.299 mi, 0.25 NM
IV. Maps represent Area, Shape, Direction and Distance, but cannot do all perfectly
A. Scale
1. nominal scale
2. scale as a ratio
3. relative scales
a. large scale => small part of Earth’s surface
b. small scale => large part of Earth’s surface
B. Properties
1. Conformality
a. retention of correct angles
b. lines of longitude and latitude cross at right angles
2. Equivalence
a. a unit of map area represents the same surface area on Earth’s
surface
b. lines of latitude ands longitude do not cross at right angles
c. direction and shape are distorted
3. Distance
‘equidistant’ maps are only relatively so
4. Direction
A straight line on these maps represents the correct great circle line