1. Topographic Maps
Lab 2

2. Concepts Map projections Map scale Topographic maps
Contour lines
Topographic profiles
Basic map elements
“map”: a representation, usually on a flat surface, of features on the earth showing respective forms, sizes, and spatial relationships

3. Map Projections Why “projections”?
A globe is the only true representation of the Earth
Have many methods of transforming the 3D Earth’s features onto a 2D flat surface
Flat maps cannot exist without a projection
Projections distort features in one of the following ways:
Size
Shape
Direction
Distance

4. Map Projections: Mercator
Mercator made allowances in this projection and opted for true shape.
But size has suffered… look at Greenland on a globe, then this map.

5. Map Projections: Peters
Peters distorts shape but gives true size in his projection.
Compare Greenland from here to Mercator’s projection.

6. Mercator vs Peters – who is right?
No single projection is ideal for all purposes.
Depending on the use of your map, choose the projection carefully.
Learn more about projections here:

7. Map Scale
Scale indicates how much the Earth has been reduced for reproduction on a map.
Ratio of the image on a map to its true size
Small vs Large scale maps
“Small scale maps” show a large area of Earth with less detail.
“Large scale maps” show a small area of Earth in great detail.

8. Map Scale: 3 Methods Written/Verbal scale
States the ratio
“One inch equals five miles”
Representative Fraction (RF) scale
Shown as a ratio or fraction
1:24,000 or 1/24,000
No units provided. *You* apply the same unit of measurement to both sides of the ratio, and it will be true.
1 inch [on the map] : 24,000 inches [on the Earth]
Graphic scale

9. Topographic Maps Older maps were 15-minute series
15’ latitude x 15’ longitude
Newer maps are 7.5-minute series
7.5’ = ¼ of the 15’ maps
Often called “quad”rangle maps
Standardized color scheme
Brown – contours
Blue – water
Black – human-made features
Green – vegetation
Red – important human-made features
Pink – urban areas
Purple – revisions/updates due to aerial photos

10. Topographic Maps: Contours
Topographic maps show the lay of the land using isolines called “contours”
Isoline = line connecting points of equal value
Contours connect points of equal elevation
A datum is a reference point from which all elevations are measured.
On topo maps, what do you think is the reference point (“zero datum”)?

11. Topographic Maps: Contours
Rules of Contour Lines
Contours are drawn at regular intervals (e.g., every 10 feet of elevation). Called “Contour Interval.”
Contours are always closed loops, though they usually travel beyond the margins of the map.
Contours never cross each other.
Where contours are close together, they show a rapid change in elevation. Where they are far apart, they show a gradual change.
Values inside a closed contour line are higher than outside the contour line.
See other rules on page 59 of your lab manual.

12. Topographic Maps: Contours
CONTOUR INTERVAL
Spacing between each contour line
This will be a consistent number.
Watch for the unit of measurement associated with the contour interval.
INDEX CONTOUR
Every 5th contour line
Indicated by a heavier line.
Helps draw your eye to certain intervals.
Allows the mapmaker to simplify the map – may only label index contours instead of every line.

13. Topographic Maps: Contours
The contour interval is marked with a specific unit of measurement.
You can see the index contours every five lines.
Contour Interval: 200 feet

14. Topographic Maps: Contours
When reading a map, all points on a contour line are the same elevation.
Otherwise, you must interpolate the point.
e.g., “a” = 104 ft
e.g., “b” = 170 ft
e.g., “c” = 196 ft
Contour Interval = 20 feet

15. Topographic Maps: Contours
Hill: represented by a concentric series of closed contours.
Depression: indicated by hachure marks on the downhill side.
Rule of Vs: Contour lines “V” upstream when crossing a stream. The point of the “V” points uphill.

16. Topographic Maps: Contours
Contours allow us to find the relief of the landscape.
Relief = difference in elevation between two points on a map
Total/Local Relief = difference in elevation between the highest and lowest points on a map

17. Topographic Maps: Profiles
Topographic maps show a birds-eye view of the landscape.
Topographic profiles show a side-view of the same landscape.

18. How to Create Profiles

19. How to Create Profiles
Elevation (m)

20. How to Create Profiles
Elevation (m)

21. Topographic Maps: Basic Elements
You should be able to
locate the following:
Map Body
Title
Location
Date
Data sources
Direction
Legend
Projection
Scale