Mapping the Earth
118 Points total
Latitude and Longitude
The Earth is divided into a grid of circular segments which are perpendicular to one another, called latitude and longitude.
Latitude lines run horizontally, and are parallel to the equator. Degrees latitude are numbered from 0° to 90° north and south. Zero degrees (0°) is the equator, 90° north is the North Pole, and 90° south is the South Pole. Latitude is commonly the first number expressed in a lat/long coordinate and is often expressed in the form of degrees, minutes, and seconds, there are 60 minutes in a degree and 60 seconds in a minute for instance: 38°47’30″N. (38 degrees 47minutes 30 seconds, north). More on this below.
Longitude lines (also called meridians) run perpendicular to latitude lines. Their spacing is widest at the equator, and converges at the Poles. The prime meridian or Greenwich Meridian (0° longitude) runs through Greenwich, England. Half way around the Earth, the degrees meet (180° east and west) in the Pacific Ocean, just west of the Midway Islands, and just East of the Fiji Islands and New Zealand. Longitude is commonly the second number expressed in a lat/long coordinate, and is often expressed in the form of degrees, minutes, and seconds.
Degrees are often divided into minutes (‘) and seconds (“). Each degree has 60 minutes and each minute has 60 seconds. Seconds can be divided further in tenths, hundredths, etc. for greater and greater precision. An example of using lat/long to describe a specific point is that the National Geographic Society in Washington, DC is located at 38°54’19” N, 77°02’14” W (38 degrees, 54 minutes, 19 seconds north of the equator, and 77 degrees 2 minutes, 14 seconds west of the prime meridian).
How to Measure Distance on the Map
The scale in the map legend provides the means for measuring distance. On USGS (United States Geological Survey) maps, the scale is given as a fraction, such as 1:24,000 or 1:100,000, and as a bar scale, which is a “ruler” divided into miles and kilometers. On a map scaled at 1:24,000, one inch on the map equals 24,000 inches (or 2,000 feet) on the ground.
True North vs. Magnetic North
Most maps are oriented to true north, meaning they are oriented along true north and south meridians of longitude. The top of the map usually points to the North Pole. The Earth’s magnetic pole is not located at the true or geographic pole. The magnetic North Pole lies south of the true North Pole, causing an error in compass readings. The angle that the magnetic needle points away from true north is called declination. What you see below is a declination diagram and it tells the difference between true north and magnetic north. In the case of this map, magnetic north is 11.5 degrees to the west of true north at this map’s location. On most modern maps North is up which means East is to the right, West is to the left and South is down.
What is a Topographic Map?
Topographic maps use contour lines to show changes in terrain and elevation, and are often overlaid with a wide variety of information, such as roads and streets, trails, land-use boundaries, tree and vegetation cover, and camping and hiking information to show how the lay of the land interacts with other natural and human-made features. Topographic maps are used for outdoor activities, engineering, energy exploration, natural resource conservation, environmental management, public works design, and commercial and residential planning.
Topographic Map Basics
It is found in the top right hand corner of the map:
Topographic maps use contour lines to portray the shape and elevation of the land. Contour lines are the curved, usually brown lines that connect points of equal elevation and make it possible for a topographic map to represent three-dimensional shapes on a two-dimensional surface. The space between the contour lines represents a set distance, called the contour interval. If the contour interval is 80 feet, for example, the vertical distance between two adjacent contour lines is 80 feet. Contour lines closer together on the map represent steeper terrain and lines farther apart represent flatter terrain. The elevation, in feet or meters, is written on darker or thicker contour lines, known as index contour lines. The contour interval can usually be found near the scale, in the map legend.
When contour lines cross a river they will make a V shape with the narrow part of the V pointing up stream
By using symbols, lines and colors, topographic maps illustrate both natural and human-made features. In order to read a map, it is important to understand what these symbols, lines and colors represent.
Each topographic map is drawn to a specific scale. A scale is the ratio of a distance between two points on a map and the actual distance of the same two points on the ground. Scale is the amount that an area or distance has been reduced in order to be included on a map. A scale of 1:250,000 means that one inch on the map is equal to 250,000 inches on the ground, or approximately four miles.
Using Latitude and Longitude on a Topographic Map
Around the perimeter of most topographic maps are small numbers showing latitude and longitude, (lat/long), with corresponding tiny lines, or ticks. By referring to the ticks and lat/long numbers you can find the exact place on the planet where you are located. The numbers on the top and bottom of the map are degrees longitude; numbers on the sides of the maps are degrees latitude. To determine the location on the map, connect the tick marks, north to south and east to west, drawing a line through your exact position on the map, and read the corresponding lat/long degrees.
The gradient is the slope of the landscape:
-When the contour lines on a map are close together the slope is steep.
-When the contour lines on a map are far together the slope is gentle.
Use the following formula to find slope (in feet per mile):
Slope = Elevation Change (feet) / Distance (miles)
Drawing Contour Lines
The process of interpolation is used to draw contour lines from a map of sounding or topographic data. Interpolation means that if, for example, you’re drawing a 20 foot contour line and you don’t have an actual point that’s 20 feet above sea level but you do have one that’s 15 and another that’s 25 you can estimate where the 20 foot line would be between those two and draw your line through that estimated point. Watch the video Drawing contour lines for more information and a demonstration of this. Contour lines are usually plotted at equal intervals, although there are exceptions.
There are a few rules for contour lines.
•Contour lines can never intersect. This would mean that one point on the surface of the Earth has two or more different elevations and that’s not possible. There is something of an exception to this rule for a perfectly vertical cliff which would be shown by multiple contour lines coming together.
•Contours can never terminate inside the map area. Go ahead and draw your contour lines until they run OFF the map. Stopping them means that there’s an area in your map that has no elevation.
•On topographic maps when contour lines cross a stream they V with the V pointing up stream this gives you a quick way to tell which way a stream is flowing on a topographic map.
•Hills on topographic maps show up as concentric circles (like a bull’s eye) but so do depressions (holes). In order to tell them apart, contours showing depressions have tick marks on them in the down hill direction called hash marks.
Hill Depression Hill with a depression on top
1)Watch the instructional video Drawing contour lines then print out the PDF file called “Contouring exercise” and draw the contour lines on the map with a contour interval of 5 feet. Photograph or scan it and turn it into the drop box. (10 points)
Base your answers to questions 2 – 10 on the topographic map of Mount St. Helens PDF file. The video Introduction to topographic maps. Will help you understand what you’re looking at.
2)What is the name of this map (quadrangle)? (3 points)
3)What is the name of the map that adjoins the North East corner of your map? (there’s a diagram on the bottom off the map) (3 points)
4)When was this map published? (3 points)
5)This map has a scale of 1:24,000 how many feet on Earth does 1 inch on the map represent? (3 points)
6)How many miles is that? (5 points)
7)What is the latitude of the Southern edge of the map (in degrees, minutes and seconds)? (3 points)
8)What is the latitude of the Northern edge of the map? (in degrees, minutes and seconds) (3 points)
9)What is the longitude on the Western edge of the map? (in degrees, minutes and seconds) (3 points)
10)What is the longitude on the Eastern edge of the map? (in degrees, minutes and seconds) (3 points)
11)What is the difference between the northern most and southern most latitude on this map (in minutes and seconds)? (5 points)
12)Why is this Quadrangle Map NOT a perfect square? (3 points)
13)What’s the contour interval of the map? (3 points)
14)What’s the elevation of the lava dome at the center of the volcano? (3 points)
15)What direction is the south fork of the Toutle River flowing? (look on the western side of the map) (3 points)
Measuring distance on our map is going to be a little tricky because we have a PDF map and not a paper map but once we make a scale we’ll be able to use it. To make a scale, follow the directions below.
•Set the magnification on your PDF to 100% (you can adjust it at the top of the window)
•Scroll down to the bottom of the map where the scale is.
•Take a piece of paper and hold it against your monitor up to the scale bar in feet.
•Make a tick mark for every 1000 feet.
Now you have a moveable scale that you can use to determine distance on the map AS LONG AT THE MAGNIFICATION IS 100
16)How far is it across the Mt St. Helens crater in feet running east west in feet? (look for where the gradient gets very steep that’s the crater) (5 points)
17)Use what you learned in module one to convert that distance in feet into miles. (5 points)
18)Generally speaking is the gradient on the North side of the volcano shallow or steep? (3 points)
19)Generally speaking is the gradient of the South side of the volcano shallow or steep? (3 points)
20)Which would be easier to walk up the North or South side? (3 points)
Let’s actually calculate the gradient on the North side of the volcano in the area called ‘The Breach’. The video Calculating a gradient will walk you through the directions below. Recall that gradient is usually expressed in feet per mile. So, for example, if the gradient is 50 feet/mile that means that for every mile you walk you travel up or down 50 feet. It will be easiest to do this if we have a scale that is one mile. So recall that there are 5280 feet in a mile.
•Add a tick mark on the scale you already made at 5280 feet (just estimate where it will be that will be close enough).
•Now look in the area called “The Breach” lay your scale down in that area make a note of the elevation at the beginning of your scale and at the one mile mark on your scale.
21)Elevation at your zero mark. _____________ Point A (3 points)
22)Elevation at one mile tick mark ____________ Point B (3 points)
23)Subtract B from A this will be the elevation change across that mile.
B-A= ____________ (3 points)
24)So the average gradient in The Breach is __________ feet/mile (3 points)
Look at the map of Lake Mary Florida to answer the following questions
25)What is the contour interval of this Map? _____________ (3 points)
26)Why is it different from the contour interval for the Mt. St. Helens map? (3 points)
27)What are all these circular bull’s eye features with hash marks? (3 points)
Latitude and longitude on a world map
Look at the world map here http://www.mapsofworld.com/images2008/world-map-with-latitude-and-longitude.jpg and answer the questions. Keep in mind that the Earth is a sphere. So when you’re looking at a flat map of the world you’re looking at the flat version of a sphere. Imagine peeling the surface off of a globe, now try to flatten it out on a table. One of two things is going to happen, either you’re going to rip it or you’re going to stretch it. How a map maker deals with this is called a projection. (Go here to see some different projections https://xkcd.com/977/ ). So lines of longitude should meet at the north and south pole and they will on a globe but on most maps they don’t because the polar regions have been stretched to make it flat.
Give the latitude and longitude of the following places. (Remember latitude first, longitude second and don’t forget to specify North, South, East, West. For Example 28N, 82W. ) Your instructors are aware that you will be estimating these values you don’t need to be exact but you should be in the right neighborhood.
28)Pinellas county (It’s not labeled on the map but we’re about halfway down the west coast of Florida.) ________________________ (3 points)
29)Tasmania (The island south of the east coast of Australia) ________________________ (3 points)
30)The center of Mongolia (Say where the “N” in “Mongolia” is on the map) ________________________ (3 points)
31)Uruguay (it’s on the east coast of South America ________________________ (3 points)
32)Certain lines of latitude have names, they are the Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and the Antarctic circle. Do a little bit of research find out where these lines of latitude are and what their significance is. (10 points)
Go ahead and print the last two pages they contain a topographic map and the grid for a cross section.
Use the map on the next page along with the grid on the page after to draw the land form’s cross-section. See the video Drawing a Cross Section. If the directions aren’t clear
•Lay a piece of paper down from A to B across the landform.
•Make a tick mark wherever your paper crosses a contour line. Also, make a note of the elevation of that contour.
•Lay your paper underneath the graph that says cross section and transfer your elevations to that graph.
•Now draw smooth line through your points. This is what the ground would look like from the side.