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 circleEach degree can be divided into 60’

minutesEach 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

0 degrees Latitude (Equator)

90 degrees North Latitude

90 degrees South Latitude

Latitude

0 degrees Longitudeat Greenwich, England

X

40o0’0”N 74o0’0”W

Topo Maps Types of contours

• 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

500

Contour Interval, Scale, Series, Sectors

Use the scale to measure distanceUNITS MUST MATCH

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 line2. Mark contours3. 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

• Initial Point• Meridian vertical • Baseline horizontal• Township 36 mi2• Range distance E or

W refer. principal meridian, ea. 6 miles

• Section 1 mi2

Washington and Oregon Initial Point

Section numbers wind back and forth,edges always have same matching number