Map Relief and Contour Features Notes

Relief Altitude

• Height is given in metres.
• Height on a map can be shown in the following ways: contour lines, trig beacons, spot heights, bench marks, hachures, and orthophotos (orthophotos).

Contour Lines

• Contour lines are brown lines drawn on a map joining places of equal height above sea level.
• Contours are drawn in 20 metre intervals on topographic maps. This interval can be expressed as $\Delta h = 20\ \text{m}.$
• If you have a contour line showing the height of $120\ \text{m}$, then the next height above that will be a contour line showing $140\ \text{m}$ (i.e., the next contour is $h<em>{n+1} = h</em>n + \Delta h$).
• Numerical examples from Page 3 (as shown in the transcript): $840\,,$ $820\,,$ $800\,,$ $-780\,,$ $-760^{\circ}$.

Trigonometric (Trig) Beacons

• Shown on topographic maps as small triangles.
• Often have two sets of figures next to them: the beacon number and the height.
• The height is always an exact height, so it will have figures after a decimal point, e.g., $135.3\,\text{m}.$
• The height is almost always placed below the number of the Trig beacon.

Example Map Features and Elevations (Page 5 content)

• The page shows labeled features and elevations such as:
  • Plateau
  • 299
  • KAITOKE LOOP
  • A30U
  • 257m
  • PLATEAU
  • 200
  • PARK HERE / Go-kart track / $352 / Airstrip / Rifle range / Gate, turn right there!
  • 378
  • Goat Rock
  • Take narrow track / apridge here / Enter bush herg / to avoid gors
  • 579
  • Tunnel
  • 7514
  • 626m
  • mutaka / Rail / tahi / River / GILBER
• These items illustrate how text, road labels, features, and elevations appear together on a map.
• Elevations present in this example include values such as $299\,\text{m}$, $257\,\text{m}$, $200\,\text{m}$, $378\,\text{m}$, and $626\,\text{m}$ (plus other numeric labels).

Spot Heights

• Spot heights are points on a map giving exact measurement and are not limited to 20m intervals like contours.
• They are indicated as black dots with numbers next to them.

Bench Marks

• Bench marks are specific heights taken next to main roads.
• Indicated by a red arrow-like symbol touching the side of the road.
• A set of figures (in black) next to the symbol gives the height.

Hachures

• Hachures are small lines used to depict relief.
• They run directly down slope.
• The thickness of the lines is proportional to the slope angle:
  • Steep slopes are portrayed by dark bands of thick and closely spaced hachures.
  • Gentle slopes are shown with thin and crowded hachures (as per the transcript).
• Hachures promote visualisation of terrain but there is potential for bias by the map-maker and for misinterpretation by the user.
• In rugged terrain, maps can become very dark, and other features may become difficult to portray.

Orthophotos (Ortophotos)

• Contours are included, but here each successive contour is a difference of 5 meters:
  • The contour interval is $\Delta h = 5\ \text{m}.$
• Spot heights are shown in the same way as on topographic maps.