Intro to Maps
Since most of you got your lab books
today, I’ll give this little introduction
Normally you are expected to study the lab
before coming to class
Points of the Compass
Degrees, Minutes, Seconds
There are 360o degrees around a circle
Each degree can be divided into 60’
minutes
Each minute can be divided into 60”
seconds
X
Global Positioning
We can use
lines parallel to
the equator and
lines between
the poles to
position objects
on the surface
30oN Lat 60oW Long
Latitude
90 degrees North Latitude
0 degrees Latitude (Equator)
90 degrees South Latitude
0 degrees Longitude
at Greenwich, England
40o0’0”N 74o0’0”W
X
Topo Maps Types of contours
500
Use the scale to measure distance
UNITS MUST MATCH
Contour Interval,
Scale, Series, Sectors
• Every point on a contour line
represents the exact same
elevation
• Contour lines can never cross
one another. Exception:
• Moving from one contour line
to another always indicates a
change in elevation.
• On a hill with a consistent
slope, there are always four
intermediate contours for every
index contour.
• The closer contour lines are to
one another, the steeper the
slope
http://geology.isu.edu/geostac/Field_Exercise/topomaps/topo_interp.htm
Contour Rules
• The rule of V's: sharp-pointed vees usually are in stream
valleys, with the drainage channel passing through the
point of the vee, with the vee pointing upstream. This is a
consequence of erosion.
• The rule of O's: closed loops are normally uphill on the
inside and downhill on the outside, and the innermost
loop is the highest area. If a loop instead represents a
depression, some maps note this by short lines radiating
from the inside of the loop, called "hachures".
• Spacing of contours: (repeat) close contours indicate a
steep slope; distant contours a shallow slope.
Making a Topo Map
• Suppose you measured elevations and positions with your GPS
• Use the Latitudes and Longitudes you measured and lay out
the elevations
• Pick an elevation you will draw
Making a Topo Map
• Pick an elevation you will draw
• Find a place with two nearby elevations, one larger, one
smaller
Making a Topo Map
• Pick an elevation you will draw
• Find a place with two nearby elevations, one larger, one
smaller
• Place a X where the elevation would lie
Making a Topo Map
• Pick an elevation you will draw
• Find a place with two nearby elevations, one larger, one
smaller
• Place a X where the elevation would lie
• Repeat and connect the X’s
Drawing a Cross-Section
(Elevation Profile)
1. Hold a sheet of paper along line
2. Mark contours
3. Write elevation next to each
• Make a vertical scale (usually exaggerated)
• Make a dot at each contour at its elevation
• Connect the dots for your elevation profile
• Later we will use these to make geologic
cross sections
• Topo Maps, Air Photo Pairs, GPS, etc
Township and
Range System
•
•
•
•
Washington and Oregon Initial Point
Initial Point
Meridian vertical
Baseline horizontal
Township 36 mi2
• Range distance E or
W refer. principal
meridian, ea. 6 miles
• Section 1 mi2
Section numbers wind back and forth,
edges always have same matching number