Comprehensive Topographic Mapping and Geographic Coordinate Systems Study Guide

Topographic Maps and Mapping Terminology

• Elevation: The distance or height of a point above sea level.

• Contour Line: A line on a topographic map connecting points of equal elevation.

• Contour Interval: The vertical distance or difference in elevation between two adjacent contour lines.

• Index Contour: A specific contour line that is labeled with its explicit elevation.

• Relief: The calculated difference between the highest and lowest elevation points on a map.

• Hachures: Specialized depression contours that represent a localized decrease in elevation.

• Cartography: The study and practice of map making. A person who creates maps is called a cartographer.

• Profile: A side view representing the vertical shape and cross-section of a landscape or terrain feature.

• Map Key: A legend or reference area on a map that shows and explains what each map symbol represents.

• Benchmark: A designated point of known, surveyed elevation.

• Contour Line Behaviors and Interpretations:

  • Steep Slope: Indicated by contour lines that are drawn very close together.

  • Gentle Slope: Indicated by contour lines that are spaced far apart.

  • Streams and Rivers: Contour lines that cross a stream form a "$V$" shape that points upstream toward the water source.

  • Intersection Rule: Contour lines can never cross or overlap one another.

  • Hills and Elevations: Displayed as closed loops. A higher density of inner closed loops indicates greater elevation.

  • Depressions: Displayed as closed loops containing hachure marks. Additional nested depression loops indicate deeper terrain.

Geographic Coordinate System: Latitude and Longitude

• Latitude:

  • Lines run horizontally from west to east (side to side).

  • Latitude lines are also referred to as parallels.

  • Measure geographic distance north and south relative to the Equator.

  • Equator: Represents $0^\bullet$ latitude.

  • North Pole: Positioned at $90^\bullet\,\text{N}$ latitude.

  • South Pole: Positioned at $90^\bullet\,\text{S}$ latitude.

  • Tropic of Cancer: Located at $23.5^\bullet\,\text{N}$ ($23\frac{1}{2}^\bullet\,\text{N}$) latitude.

  • Tropic of Capricorn: Located at $23.5^\bullet\,\text{S}$ ($23\frac{1}{2}^\bullet\,\text{S}$) latitude.

• Longitude:

  • Lines run vertically from north to south (up and down).

  • Longitude lines are also referred to as meridians.

  • Measure geographic distance east and west relative to the Prime Meridian.

  • Prime Meridian: Represents $0^\bullet$ longitude and runs directly through Greenwich, England.

  • Standard Meridians: Measure from $1^\bullet$ to $179^\bullet$ East and West of the Prime Meridian.

  • International Date Line: Positioned at $180^\bullet$ longitude, marking the boundary where a new calendar day begins.

• Map Orientation and Coordinates:

  • Northern-most parallel defines the upper boundary of a map layout.

  • Southern-most parallel defines the lower boundary of a map layout.

  • Western meridian defines the left boundary of a map layout.

  • Eastern meridian defines the right boundary of a map layout.

Global Time Zones and Navigation

• World Time Zones:

  • The Earth is divided into $24$ individual time zones worldwide.

  • Each individual time zone corresponds to $15^\bullet$ of longitude ($360^\bullet / 24 = 15^\bullet$).

• United States Time Zones:

  • The $48$ contiguous states encompass $4$ time zones.

  • The entire United States encompasses $6$ total time zones.

• International Date Line Traversal:

  • Traveling west across the International Date Line requires advancing the calendar by $1$ day.

• Time Calculation Application:

  • If the time is $1:00$ in Richmond, Virginia, the corresponding time in Seattle, Washington is $10:00$ ($3$ hours earlier).

Map Projections and Map Scale

• Quadrangle Maps:

  • A $7.5$ minute quadrangle map spans $7.5$ minutes ($7\frac{1}{2}$ minutes) of distance in latitude and $7.5$ minutes ($7\frac{1}{2}$ minutes) of distance in longitude.

• Map Scale Ratios:

  • A map scale of $1:24,000$ indicates that $1$ unit on the map represents $24,000$ of the same units on the ground (units may be measured in inches, feet, or any other unit).

• Mercator Projection:

  • Longitude lines are drawn parallel to each other.

  • Shows accurate direction, but distorts landmass sizes severely near the polar regions (e.g., Greenland and Antarctica).

• Conic Projection:

  • Constructed by projecting a globe onto a cone of paper touching a line of latitude.

  • Yields less spatial distortion, making it suitable for smaller areas.

• Robinson Projection:

  • Exhibits reduced overall distortion across geographic areas compared to cylindrical projections.

Maps Review Questions and Answers

• Question 1: Which type of map shows elevations?

  • Answer: Topographic map or contour map.

• Question 2: Which way do latitude lines go?

  • Answer: East to west (side to side).

• Question 3: What is another name for latitude lines?

  • Answer: Parallels.

• Question 4: Which directions do you give with latitude lines?

  • Answer: North and south.

• Question 5: Which way do longitude lines go?

  • Answer: North to south (up and down).

• Question 6: What is another name for longitude lines?

  • Answer: Meridians.

• Question 7: Which directions do you give with longitude lines?

  • Answer: East and west.

• Question 8: Explain what the ratio $1:24,000$ means on a map?

  • Answer: $1$ unit on the map is $24,000$ units on the ground (the unit can be any amount, such as inches, feet, etc.).

• Question 9: What is a benchmark?

  • Answer: A place of known elevation.

• Question 10: What does a hill look like on a topographic map?

  • Answer: A closed loop; more loops mean it is higher.

• Question 11: What does a depression look like?

  • Answer: A closed loop with hachure marks; more depressions mean it is deeper.

• Question 12: What are the major differences between Mercator map projections and conic map projections?

  • Answer: Mercator map has longitude lines made parallel; Conic paper touches a globe on a line of latitude.

• Question 13: How do you know where the land is steep?

  • Answer: Contour lines are closer together.

• Question 14: What can contour lines never do?

  • Answer: Contour lines can never cross.

• Question 15: What happens when you cross the International Date Line going west?

  • Answer: Advance $1$ day.

• Question 16: If this was a topographic map, label which line would be the northern-most parallel, the southern-most parallel, the western meridian, and the eastern meridian.

  • Answer: Top edge is North (northern-most parallel), bottom edge is South (southern-most parallel), left edge is West (western meridian), and right edge is East (eastern meridian).

• Question 17: What is the twenty-three and one-half degrees southern latitude and northern latitude?

  • Answer: Southern latitude is the Tropic of Capricorn ($23.5^\bullet\,\text{S}$); northern latitude is the Tropic of Cancer ($23.5^\bullet\,\text{N}$).

• Question 18: What do contour lines do when they cross a stream?

  • Answer: They create a $V$ shape that points upstream.

• Question 19: What city does the Prime Meridian run through?

  • Answer: Greenwich, England.

• Question 20: What is the name of a person who makes maps?

  • Answer: Cartographer.

• Question 21: What type of map shows accurate directions but distorts places like Greenland and Antarctica?

  • Answer: Mercator.

• Question 22: What kind of map has less distortion but shows smaller areas?

  • Answer: Robinson.

• Question 23: What is the correct latitude for the north and south poles?

  • Answer: $90^\bullet\,\text{N}$ and $90^\bullet\,\text{S}$.

• Question 24: If it is $1:00$ in Richmond, Virginia, what time is it in Seattle, Washington?

  • Answer: 10:00$.\n* Question 25: What is meant by a 7.5 minute quadrangle map?\n * Answer: It has 7.5$minutes of latitude and$7.5$$ minutes of longitude.