Transcript Introduction to Topographic Maps

Topographic maps
Rules for contours
1. The coastline is the 0th contour.
2. Crossing a contour requires a change in elevation
(you must be going up or down).
3. Contours cannot cross one another.
4. Adjacent contours can be:
1. the same value
2. one contour interval different (higher or lower) or
5. If adjacent contours have the same value the ground
between them is either:
1. going up a little (thought not more than a contour interval)
and then back down (i.e., a “hill”) or
2. going down a little and then back up (a “depression”).
Examine the surrounding contours to clarify which is
the case.
Rules of contours
6. The closer the contours, the steeper the slope. A
truly vertical cliff is shown by overlapping
contours. Cliffs are rarely vertical for any
significant height.
7. A closed contour with tick marks indicates an
enclosed depression. The tick marks are drawn
on the “down” side (i.e., they point into the
depression).
8. Not all depressions will have contours with tick
marks. Other features, such as a lake within the
contour (depression) or adjacent hills, will
clarify the situation.
Rules of contours
9. As you move perpendicularly away from a stream
you must be going uphill (i.e., out of the stream
valley).
10.In a valley, the contours have a “v” shape with
the point of the “v” pointing upstream.
11.On a profile, if you start and finish at the same
elevation you must cross each contour an even
number of times (“what goes up must come
down”).
12.The last contour you pass on the way up (or
down) is the first one you pass on the way down
(or up, respectively)
90
Reading
contours
110
120
The contours
“v” upstream
(rule 10)
130
140
130 m
100 m < B < 110 m
Reading
contours
… and here I
am below X m
…this must be…
But here I am
above X m …
and going
“A…
” must
clearlydown
…And
behere
higher
thanhere
35 I must
be above 35 m.
…
if it
I’must
m going up
…So
but
Here I must be
here…
also be lowerbelow 35 m.
And “B” must be
than 40, or there
below 35 m but
would be another
above 30 (or
contour.
there would be a
30 m contour
X
35
30
25
35 m < A < 40 m
30 m < B < 35 m
Drawing Contours
30 m
20 m
10 m
0m
Page 2 map
•
•
•
•
The spot heights are in metres
Draw contours at 10 m intervals
Label the contours
The 180 m contour is drawn for you
Learning objects
• Throughout the lab you can/will use various
Flash™ animation files on aspects of
topographic files.
• They are not embedded in this PowerPoint
file.
• You should download them to you own
computer for use at any time (including
tests!)
• They are on Socrates at:
– http://socrates.acadiau.ca/courses/geol/1013/labs/LearningObjects.htm
Topographic map features
• The LO shows you the Wolfville sheet – a
typical 1:50 000 sheet
• After opening the LO, mouse over any of
the blued areas to show the features of the
map in more detail.
Wolfville sheet LO
Scale
• Scale is represented as a ratio and shows the
relationship between a distance on the map
and the distance on the ground.
– 1:20 indicates that one unit on the map is the
equivalent to 20 units on the ground
– 1:50,000 is the scale of the map you’ll be
looking at today
– The bigger the second number the smaller the
ratio (fraction) = small scale.
Scale LO
“North”
• On a standard map there are three north
directions
– Magnetic north (the direction to the magnetic
north pole)
– True north (the direction to the north
geographic pole)
– Grid north. On Canadian topo maps there is a
reference grid that is not the same as the other
north directions.
Declination
• True north = rotational pole.
• Magnetic north pole is not the same as
rotational pole. Currently the magnetic pole
is in the Canadian Arctic Archipelago. And
it moves!
• For most locations on the globe there is a
difference in direction between magnetic
north and true north called the “magnetic
declination”.
Declination
• Declination in Eastern Canada is westward,
in Western Canada it is eastward.
• Shown on side of the map with a date and a
rate of change (because mag. north pole
“wanders”).
• Allows you to calculate the declination at
any given date.
Declination at Wolfville
Declination for Wolfville sheet in … … 2011
Latitude and Longitude
• Latitude = angular distance north (or south)
of the equator.
• Longitude = angular distance east or west of
the “prime” meridian (Greenwich, England).
• Halifax (Citadel), is approximately:
– 44° 38’ N and 63° 35’ W.
Latitude and Longitude
• Latitude
– angular distance / linear distance is constant
– 1° latitude at equator = 1° latitude near poles
(=111 km)
• Longitude
– angular distance / linear distance is NOT
constant
– 1° longitude at equator is ca. 111 km.
– 1° longitude at Wolfville is ca. 81 km.
– 1° longitude at the north pole = 0 km
UTM grid
• UTM grid designed so that the coordinates
are the same linear distance in both
directions (E-W and N-S).
• UTM grids are the pale blue lines across the
map.
• UTM coordinates are in meters.
Determining UTM coordinates
• Use the Learning Objects.
Easting LO
Northing LO
Drawing a cross section
• Another Learning Object
Drawing a cross section LO
Legibility!!!!!!!
• Use a pencil!
• Use an eraser if you make a mistake!
• These are NEW maps. Do NOT write on
them!
• Write in full sentences where it’s called for!
Questions?