Introduction to Map Use

study outline – projections

You should be able to:

1. list and describe he major and minor properties of a map projection

2. describe the physical process of making a map projection using paper, a light and a globe

3.

A. definition of a map projection – the process used to represent a round world on a flat map

B. Conceptually, we can think of a projection as using a light inside or behind a globe to project the image of the globe onto a paper wrapped around the globe in some fashion.

1. The results of a projection will vary according to:

i. the position of the light source

ii. the shape and location of the paper

(1) shape of paper

(a) plane

(b) cylinder

(c) cone

(2) point(s) of contact between paper and globe

(a) the point of line of contact (tangency) is the area of least distortion for most projections.

(b) many projections that are very good at the point or line(s) of tangency are greatly distorted away from the tangent.

(3) orientation of paper allows the projection to be tangent to the globe in the area of interest

2. In practice a map projection is a mathematical process that links every latitude and longitude to a point on the paper. Many projections are difficult to conceptualize with paper and lights.

C. possible properties of a map projection. No map can have all off these!

1. major properties -- properties that can be true for the entire map

i. preserves shape – conformal

(1) at any point has the same scale in all directions

(2) latitude and longitude lines meet at right angles

ii. preserves area – equivalent

2. minor properties – can be true only for part of a map

i. true distance

ii. true direction

3. many projects have none of these properties.

D. distortions

1. the distortions introduced by a projection can affect our perception of the world. We need to be aware that every map is distorted to some degree in some of these properties