topographic maps 1 Flashcards
what is a topographic map?
a 2-dimensional representation of a 3-
dimensional land surface (LANDSCAPE)
what are contour lines?
Lines of equal elevation (above sea level)
on a TOPOGRAPHIC MAP
what are some characteristics of contour lines?
✓ indicate height or elevation on TOPOGRAPHIC MAP.
✓ each point on CONTOUR LINE has same elevation.
✓ LANDFORMS (e.g., hills, valleys, slopes, coastlines).
✓ RELIEF (differences in elevation)
what is a quadrangle?
Section of Earth’s surface bounded by
LINES of LATITUDE (at top or north and bottom or south) and LINES of LONGITUDE (at left or west and right or east)
North always at top of QUADRANGLE and represents direction of TRUE NORTH, abbreviated GN (grid or geographic North Pole)
are magnetic compasses attracted to the true north?
no, magnetic compasses are attracted to magnetic North Pole or COMPASS NORTH (abbreviated MN) and NOT TRUE NORTH
what is declination?
difference in degrees between COMPASS
NORTH (MN) and TRUE NORTH (GN).
Magnetic (or COMPASS NORTH) migrates and therefore DECLINATION at specific site changes over time
how is elevation expressed?
Elevation (i.e., HEIGHT) is expressed using the
CONTOUR LINES
what are index contour lines?
CONTOUR LINES that are drawn thicker and that have ELEVATION printed on them
what are some of the characteristics of index contour lines?
✓ labelled with elevations that consistently increase (or decrease) by same amount/increment.
✓ enable reader to determine CONTOUR INTERVAL
what are the characteristics of contour interval?
✓ increase or decrease in elevation between any two contour lines
✓ remains constant for any given CONTOUR MAP
= ELEVATION CHANGE ÷ NUMBER OF CONTOUR LINES
= 300 units ÷ 3 contour lines
= 100 units.
what does an elevation of 0 units mean?
sea level
what are the contour line rules?
- Every point on a CONTOUR LINE has SAME ELEVATION. CONTOUR LINES effectively connect points of EQUAL ELEVATION
- Use INTERPOLATION to ESTIMATE ELEVATION at a POINT B located IN LINE between POINTS A and C of KNOWN ELEVATION.
- Use EXTRAPOLATION to estimate ELEVATION at POINT C located IN LINE and beyond POINTS A and B of known ELEVATIONS.
- CONTOUR LINES separate points of HIGHER ELEVATION (uphill) from points of LOWER ELEVATION (downhill).
- CONTOUR LINES always close to form an IRREGULAR CIRCLE.
- CONTOUR INTERVAL: Elevation change between any two adjacent CONTOUR LINES of different elevation on map.
- CONTOUR LINES never cross each other!
- CONTOUR LINES never merge!
- EVENLY SPACED contour lines of different
elevation represent a UNIFORM SLOPE. - The closer CONTOUR LINES are to each other, the STEEPER the SLOPE.
- A CONCENTRIC (quasi-circular) series of closed CONTOUR LINES represent a hill or mountain.
- In case of a DEPRESSION, CONTOUR LINES
have HACHURE MARKS on the DOWNHILL SIDE. - CONTOUR LINES form a V pattern when crossing streams or rivers or creeks.
- CONTOUR LINES occurring on OPPOSITE SIDES of a VALLEY or RIDGE always occur in PAIRS.
how do you Use EXTRAPOLATION to estimate ELEVATION at POINT C located IN LINE and beyond POINTS A and B of known ELEVATIONS?
To do so, use distance between POINTS A and B as a RULER or graphic BAR SCALE to ESTIMATE ELEVATION at POINT C.
how do contour lines separate points of higher elevation (uphill) from points of lower elevation (downhill)?
To determine ELEVATION at a specific CONTOUR LINE adjacent to an INDEX CONTOUR LINE determine which direction on map is HIGHER and which is LOWER.
ADD CONTOUR INTERVAL to adjacent ELEVATION (if going uphill)
SUBTRACT CONTOUR INTERVAL from adjacent
ELEVATION (if going downhill).
how are contour lines always close to from an irregular circle?
Part of CONTOUR LINE may extend beyond TOPOGRAPHIC MAP area, in which case entire IRREGULAR CIRCLE may not be seen.
what is the index contour line?
Heavier (bolder) CONTOUR LINES
labelled with corresponding ELEVATION.
Often, every 5th CONTOUR LINE is an INDEX CONTOUR LINE (this may vary).
what is the exception of contour lines never cross each other?
if have OVERHANGING CLIFF
what is the exception of contour lines never merge?
CONTOUR LINES merge into single
CONTOUR LINE if have VERTICAL CLIFF.
what does contour lines that are further from each other mean?
GENTLER (LESS STEEP) the SLOPE
what is the difference between concave and convex?
concave=hole
convex=bombé
what happens if you have concave cliff/slope?
If have CONCAVE CLIFF/SLOPE, CONTOUR
LINES will be closer together at HIGHER
ELEVATIONS and further apart at LOWER
ELEVATIONS.
what happens if you have convex cliff/slope?
CONTOUR LINES will be further apart at HIGHER ELEVATIONS and closer together at LOWER ELEVATIONS.
what do concentric and closed contour lines mean?
hill or mountain
what is depression?
A landform sunken or depressed below the surrounding area.
or
an area of land that has a lower elevation (lower elevations) than the surrounding area.
