Class 3a: The Round Earth

Map Projections

http://www.youtube.com/watch?v=n8zBC2dvERM

Map projections

• Project a round globe onto a flat surface

• Options?

• Stretch out some areas

• Cut out some areas

• Shrink some areas

Map projections

• Three properties to consider

– Size- Area (equal-area or equivalent)

– Shape (conformal)

– Distance (equidistant)

– Choose two out of three

• How large an area?

• Purpose of the map

• Ulterior motives?

What is in a picture?

• Example: The Mercator projection has straight meridians & parallels that intersect at right angles, as opposed to the Robinson projection.

– Mercator preserves area only at the equator and at two standard parallels equidistant from the equator.

– The Mercator projection is often used for marine navigation as all straight lines on the map are lines of constant azimuth.

– Any one projection cannot simultaneously preserve all these qualities of the world: shape, area, direction, and distance.

This is what happens when projections mix!

• Notice the boundary lines do not line up

• Points that are placed on the wrong projection will be misaligned as well

Cylindrical projections• Shapes are preserved• But not area!• Mercator projection

• Great Circle• Deliberate distortion?

– Cold War

– Colonialism

A Satellite View

Africa’s Size

# Second largest continent 11,700,000 sq. mi.

# 10% of the world’s population.

# 2 ½ times the size of the U. S.

5000

M

ILES

4 6 0 0 M I L E S

Cylindrical projections: Gall- Peters

• Adjusting Mercator for a more “just” map

• Also preserves area

• Distorts shape differently

Conic projections

• Best for hemispheres or small regions

• Area and shape only slightly distorted

Planar projections

• Equidistant; good for navigation

• Only good for one hemisphere

• Distorts area, not shape

Other projections• Based on more

complicated math

• Interrupted, oval, combination

Goode

Robinson

Dymaxion

Context: Why GIS?

• Many of the issues in our world have a critical spatial component!– Land management– Property lines, easements, right of ways– Data on land values, taxation, assessment– Business site selection, advertising– Proximity of ‘our’ land to other facilities (pollution,

hunting, municipal, federal, state)• “I don’t know what’s over that hill” is a common problem.

What is adjacent to the land we are using?

The Space on Earth

• The Earth is finite!– If not now, within our lifetimes there may be no

natural ecosystems. – Land managers, natural resource workers, and

politicians are and will continue to make decisions about biological systems.

– Good information and tools are needed to do this.

Enter GIS

• A computer-based tool for holding, displaying, and manipulating huge amounts of spatial data.

High End 3-D Representation

• Surfaces are made from Triangular Irregular Networks (TIN) that interpolate 3-D surfaces from 2-D contour values.

• Uses: – Hydrology: surface and

underground flows

– Line-of-Sight analysis

– Pollution Plume tracking

– Customer analysis

– Soil erosion potential

• How many data points are contained in this image? Thousands? More?

– Even without statistical measurement (which can be done) the pattern of pollution can be seen. Location and density of wells is also clear.

– Line of sight analysis allows us to determine where to put a house or power plant where it could or could not be seen from major roads. Notice the roads actually track up the hills on the right side of the image.