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
Degrees, Minutes, Seconds
There are 360o degrees around a circleEach degree can be divided into 60’
minutesEach minute can be divided into 60”
seconds
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
• 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
• Connect the dots for your elevation profile
• Later we will use these to make geologic cross sections
• Topo Maps, Air Photo Pairs, GPS, etc