1. Portraying Earth Data types File types
Lecture 2
Portraying Earth
Data types
File types

2. Portraying Earth Globes vs. Maps – 3D vs. 2D Shape – size Lat/Long:
what is it
what units
Projections:
why do we need them
what do they do
Scale
Map essentials

3. Size & Shape of Earth Diameter = 8000 miles Radius = 4000
Circumference = 25,000
Earth slightly flattened at poles - wider at equator

4. Latitude/Longitude
Latitude and Longitude define site location on the surface of the earth
Latitude is used to express distance north or south of the equator
Longitude shows east-west distance from the Greenwich 0° to the International Date 180°
Locations are given in degrees, minutes, seconds or degrees and fractions of degrees
For example:
Boston, MA: Lat 42.37N – Long 71.03W
Boston, MA: Lat 42° 22’ 11” - Long 71° 1’ 47”
Lawrence, MA: Lat 42.72N – Long 71.12W
Lawrence, MA: Lat 42° 43’ 12” - Long 71° 7’ 12”

9. Map Projection A system based on mathematical computation
It transforms the round surface (3D) of the Earth to display on a flat surface (2D), i.e. a map.
Called ‘projection’ because it was originally a question of ‘projecting’ the grid (lat & long lines) onto a sheet of paper graphically.
It is impossible to portray a curved (3D) surface on a flat (2D) map perfectly
There is always distortion
There is NO perfect projection

10. Why Projections?
The main objective is to preserve either the shape of the land or the area of the features - you can’t have it both ways!
The following slides show different projections

11. Conic Projection
Globe with light at center, projects images onto paper cone – when paper laid out flat, conic projection.

12. Plane Projection Azimuthal projection Plane projection
Globe with light at center, projects images onto adjacent paper plane (flat surface) – when paper is removed, you have:
Azimuthal projection
Plane projection
Zenithal projection

13. Cylindrical Projection
A globe with light in center projects onto paper cylinder – when paper laid flat, you have a cylindrical projection.

14. Equivalence vs. Conformality
The central problem, when constructing a map is choosing the projection.
We must think about what is being shown; what part or how much of the earth is to be mapped?
Equivalence = size
Conformality = shape

15. Equivalence
Equivalent projection is also called an equal area (size) projection
Misleading impressions of size are avoided
Good for showing distributions of geographic features
Problem: on small scale (large area) world maps - shapes of land masses are disfigured

16. Conformality Angular relationships are maintained
Shape of land mass on map is same as shape on Earth
All meridians and parallels cross at 90° angles – right angles.
Problem: the size of an area is considerably distorted to portray the proper shape.

17. Mercator Projection is the most well known projection
is a special purpose map projection used for navigation
has area distortion
is conformal, i.e. preserves shape, not size
is the only map projection that shows true compass bearings for navigation
straight lines on a Mercator projection will always intersect longitude lines at the same angle - Mercator is the only map projection that does that

18. MERCATOR
PRO JECTION

19. Note the size of South America and Greenland
South America = 17,819,000 sq km
Greenland = 2,166,086 sq km
Note the size of South America and Greenland
Conformal projection — preserves shapes

20. How does North America compare between these three projections?
Mercator
Conic
Note how the lat-long lines are aligned in each of the projections.
Azimuthal

21. Equal Area Projection Why is it used here?
How do South America & Greenland compare in area?
(p. 92)

22. Shows distribution of habitable and non-habitable land
Equal Area Projection
Shows distribution of habitable and non-habitable land

23. Large and Small Scale Maps
A small scale map shows a larger area with little detail and has a large denominator 1:250,000
A large scale map shows a smaller area with more detail has a small denominator 1:500 or 1/500

24. A map with a scale of 1:10,000,000 would be considered small scale when compared with a map of 1:1,000.
This is a small scale map – there is no detail shown.
There is such great area – the whole earth – it must be small scale.
i.e. 1 inch must be equal to millions of inches on the earth!

25. Data types Two basic types of data: Vector Points Lines Polygons
Raster
Grid composed of cells i.e. an array pixels arranged in rows and columns each with its own value

26. Vector data A vector based system displays graphical data as points,
lines or curves, or areas with attributes.

27. Raster data
A raster based system displays, locates, and stores graphical data by using a matrix or grid of cells.

28. File types & extensions
Shapefiles
.shp
Layer files
.lyr
Raster files
.jpeg
.tiff
.gif
.sid
Database files
.dbf
ArcMap document
.mxd

29. Databases
Excell
Access

30. Acronyms & terms Lat/long Large scale vs. small scale
Raster vs. vector
.shp
.dbf
.lyr
.mxd