Lab 1: Projection

Yingjie Hu

What is a projection?

• A projection is the rendering of the earth’s round, three-dimensional surface onto a flat map.

Projection

What do we need to make a projection?

• A surface• A method to project the features of the earth

on our surface

Surface

• Plane surface• Azimuthal projection (planar projection)

Surface

• Cylinder • Cylindrical

Surface

• Cone• Conic

How to project? Surface aspect

• Equatorial

Surface aspect

• Transverse

Surface aspect

• Oblique

Surface aspect

• Polar

Tangency

• Definition– Location at which the projection surface and the

globe touch.

Secancy

• Definition– Location at which the projection surface cuts

through the globe

Distortion

• The earth has a curved surface. When transforming the round globe to a flat surface, we will inevitably lose accuracy at places where the “paper” doesn’t touch the globe.

Map properties

• Conformality (Conformal projection)– Retention of correct angles on a map– Retaining the shapes and directions of the

features on the earth– Lose the accuracy of area– Applied in navigation

Map properties

• Equivalence (Equivalent projection)– Retention the accuracy of the area on a map– Lose shape and direction of the features on the

globe– Applied in area calculation

Map properties

• Compromise projections– Neither conformal nor equivalent– Avoid extreme distortion of one map property

Map properties

• Short summary– Distortion is inevitable, since the globe is round

while paper is flat.– Preserving one property (shape) results in the

distortion of another property (area).– Conformality retains shape and direction, but it

loses area accuracy. Equivalency has the opposite properties.

How can we get the projection information from a map?

• Surface type– From the shapes constituted by longitudes and

latitudes

Cone

How can we get the projection information from a map?

• Surface type– From the shapes constituted by longitudes and

latitudes

Cylinder

How can we get the projection information from a map?

• Surface type– From the shapes constituted by longitudes and

latitudes

Plane

How can we get the projection information from a map?

• Surface aspect– From the area focused by the map

Polar

How can we get the projection information from a map?

• Surface aspect– From the area that has the least distortion.

Equatorial

How can we get the projection information from a map?

• Surface aspect– From the area that has the least distortion.

Transverse

How can we get the projection information from a map?

• Surface aspect– From the area that has the least distortion.

Oblique

How can we get the projection information from a map?

• Conformality – The shape is preserved.– The area of the features is distorted.

How can we get the projection information from a map?

• Equivalence– The area is preserved.– The shape of the continents is distorted.

Assignment

• All the materials are on Gauchospace.• Answer all the questions, print your answer

sheet, and submit it in the next lab class.• Due date: Oct. 6th (Next Thursday).• Homework which is turned in late will lose

10% of the full score each weekday. Homework which is submitted after 5 weekdays will not be accepted.