AIM: How do we recognize different terrain features on a topographic map?

DO NOW: What is the difference between a contour interval and an index contour?

AGENDA: • Quiz #2 Make-up for Friday’s absentees. • Distribute graded HW assignments. JupiterGrades updated.

• PSAT Tomorrow – arrive at 7:15 AM with ID, #2 pencil, calculator. 10/16/13

Earth Science

1

DO NOW: What is the difference between a contour interval and an index contour?

•  A contour interval tell you the difference in elevation between consecutive contour lines. •  An index contour labels actual elevation value on a topographic map (for reference). –  Usually every 4th or 5th contour lines.

Topographic Maps •  Contour Interval – difference in elevation between each line. MUST be equal spacing. Contour interval = 20 feet

580 560 540 520

Topographic Maps •  Index Contour – Usually every 5th line is printed darker and has an elevation printed on it.

Real World

Contour Map

Rules for Contours 1.  Contour lines never cross

Rules for Contours 2. Contours form closed loops (even if not shown of the map.

Rules for Contours 3. Contours bend upstream (uphill) when crossing a stream.

Rules for Contours 4. 

The maximum possible elevation for a hill is 1 less than what the next contour should be. 90

The highest possible elevation of the hill is just below the value of the next line that is not shown

80 70 60 50

399

179

239

Closely Spaced Contours •  Steeper Slope (Gradient) – contour lines are closer together.

Wide Spaced Contours •  Gradual/Gentle Slope (Gradient) – contour lines are farther apart.

A

B

Depressions •  Contour lines which show a depression, crater, or sinkhole on a map. •  Shown by dashed lines (hachure marks) on the inside of a contour line •  The elevation of the first depression contour is the same as the lowest regular contour near it.

Rules for Contours The lowest possible elevation for a depression is 1 more than what the next contour should be.

90

90 80

The lowest possible elevation of a depression is just above the value of the next line that is not shown

51

70 60 50

Benchmarks •  a location whose exact elevation is known and is noted on a brass or aluminum plate. •  bench marks are shown on maps by an X with the letters BM written next to them.

Major Terrain Feature - A saddle is a dip or low point between two areas of higher ground. A saddle is normally represented as an hourglass

Major Terrain Feature - A cliff is a near-vertical feature that has a such steep slope that the contour lines converge into one. The last contour line has tick marks pointing toward low ground.

Major Terrain Feature - A valley is a stretchedout groove in the land, usually formed by streams or rivers. Contour lines forming a valley are either U-shaped or V-shaped. The closed end of the contour line (U or V) always points upstream or toward high ground.

Major Terrain Feature - A ridge is a sloping line of high ground. Contour lines forming a ridge tend to be U-shaped or V-shaped. The closed end of the contour line points away from high ground (contrary to normal case).

Assessment: Reading the Contour Lines: 1. Which way is the upstream? 2. Locate the index contour lines. 3. What is the difference in elevation between any 2 contour lines? 4. Find the 2 benchmarks w/ their elevations. 5. Where are the locations of 2 depression centers?