2021 Lab 1 Topo Map Introduction PDF

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This is what was covered in the first lab...

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GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

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Lab 1 – Map Systems, Topographic Maps and Contour Maps Lab Preparation: -Read through the introduction to the lab

Objectives: 1. To enable you to ‘read’ a topographic map and visualize the appearance of the area it represents. 2. To introduce common map grid systems and how to locate features using them. 3. To enable you to construct a simple topographic profile. 4. To construct a simple map of topographic elevations. 1.1 Topographic Maps A topographic map is a map that shows the size, shape and distribution of features of portions of a body’s (Earth, Moon etc.) surface. Such a map is a two-dimensional (2-D) representation of the threedimensional (3-D) surface of that portion of the body’s surface. Information on a topographic map includes: a scale, a north arrow, a reference system (usually a grid system), the contour interval, and a legend of the symbols used on the map. Other information often included is the date of construction (or publication), the name of the person, company or branch of government responsible for the construction of the map, a map name, a map reference number, an index map (indicating the location of the topographic map with respect to well known features or adjoining topographic maps), and the method of survey. Several of these points are discussed below. 1.1.1 Scale A map scale denotes the relationship between the horizontal distance measured between two points on a map and the actual horizontal distance measured on the ground. The scale may be expressed either in words, by a statement such as ‘one centimetre to 50 kilometres’ or as a representative fraction (1/ 5 000 000 or 1:5 000 000). Note that in the fractional notation used below, one unit of linear measurement on the map is equivalent to 5 000 000 of the same units on the ground. In other words, 1” = 5 000 000”, or 1 cm = 5 000 000 cm. The scale is also usually represented by a bar scale (Figure 1-1) which enables distances on the map to be directly measured and read off as distances on the ground.

Figure 1-1 Scale notations on a map

GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

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Topographic maps for all of Canada are available at scales of 1:1 000 000, 1:250 000 and 1:50 000. Around major centres (e.g. Calgary or Lethbridge) maps are also available at 1:25 000. NOTE: a small scale map depicts a larger area than a large scale map of the same dimensions. 1.1.2 North Arrow A north arrow, or some method by which north may be determined (such as lines of latitude and longitude), must appear on the map so that the map may be oriented with respect to the area it represents. Reference is often made on the map to ‘True North’, ‘Magnetic North’, and less often, ‘Grid North’. If only one arrow is given, it will be that of true north. When using topographic maps onto which a grid system has been drawn, it is often convenient to use grid north.

Figure 1-2 Topographic map arrow showing ‘Magnetic’, ‘True’ and ‘Grid’ North

1.1.3 Contour Lines (and Contour Intervals) In order to show the 3-D form of the land surface on a 2-D topographic map, contour lines are used. Topographic contour lines connect points of equal elevation on the map and may be thought of as resulting from a series of equally spaced horizontal planes cutting through an area’s surface features (hills, valleys, etc.). Contour lines are constructed at some constant vertical interval. This is called the contour interval (C.I.) and its value will depend on the detail desired and on the scale of the map. Construction of topographic maps can be tricky at times. If you provide the same data to five different people with no constraints to contouring methods, you are guaranteed to get five different depictions of the topography. Luckily the construction and reading of contour lines are subject to several rules that constrain their placement. Figure 1-3 lists 14 rules for contour lines that are to be followed when dealing with any topographic map.

GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

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Figure 1-3 Rules for Contour Lines (from: Laboratory Manual in Physical Geology, Ed. Busch, 2007)

Figure 1-4 represents a landscape that has been intersected by horizontal planes at 20 m intervals. This image at the top of the page is a perspective view of the area. The map at the bottom of the page is a topographic map consisting of contour lines, with the C.I. = 20m. Each line connects points of equal elevation all around the area so that the 3-D configuration of the area is represented.

GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts When looking at Figure 1-4, consider how the rules of contour lines from Figure 1-3 are applied to help properly project the topography.

Figure 1-4 Perspective View of a Landscape and Topographic Map (modified from Laboratory Manual in Physical Geology, Ed. Busch, 2007)

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GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

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1.1.4 Elevation This refers to the vertical distance above some datum, usually sea level. to determine the elevations of points on a topographic map, sometimes points do not lie exactly on contour lines so their elevations must be estimated from their proximity to the bounding contour lines. Refer to rules #2 and #3 from Figure 1-3 to accomplish this. 1.1.5 Relief This is the difference in elevation between the highest and the lowest points in the area under consideration, 1.1.6 Gradient This is a measure of the steepness of some particular slope and is usually expressed as the difference in elevation per unit horizontal distance (usually m/km or ft/mi). 1.1.7 Slope In various engineering problems, slope is expressed in one of the following ways: 1. As a slope angle 2. As rise per unit run (the tan of the slope angle) 3. Rise as a percent of run 4. As run per unit rise (the cotan of the slope angle) 1.2 Topographic Profiles (Cross-Sections) A topographic profile shows the intersection between the topographic surface and a vertical plane. It shows the ups and downs of the topography along the line of profile and is simply a graph of vertical elevation versus horizontal distance. Constructing Topographic Profiles 1. Locate the selected line of profile on the map (line A-A’ of Figure 1-5). Note: Only mark the profile line on the maps in the labs with the appropriate pens. 2. The edge of a piece of paper (Figure 1-5 step 2) is laid along this line and the following points marked: a) the beginning and the end of the profile b) the points where contour lines cross the line of the profile A-A’. c) the elevation values for the contour crossings are recorded next to the points on the paper. 3. This information is transferred to a separate sheet as shown in Figure 1-5 step 3. Note that the lowest elevation on the profile is selected to be slightly lower than the lowest elevation crossed on the profile line. The profile is completed by connecting the points, taking into consideration the interpolated elevations between the points as shown by the contour map.

GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

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Once constructed, it is necessary to label the ends of the profile (A and A’ in this case). Commonly, important features are also labeled, such as major rivers and important ridges and peaks.

Figure 1-5 Construction of a topographic profile (cross-section) (from: Laboratory Manual in Physical Geology, Ed. Busch, 2007)

NOTE: Topographic profiles should never be depicted as sharp connecting lines. It is meant to be indicative of true topography so a gently cured line should be used to connect all points (Figure 1-6).

GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

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Figure 1-6 Incorrect and correct methods of creating a topographic profile line

1.2.1 Vertical Exaggeration (V.E.) The vertical and the horizontal scales used in construction of the profile must appear somewhere on the profile. Whenever possible profiles should constructed such that the two scales are equal. If not equal, then vertical exaggeration occurs, resulting in distortion of the profile and the inclination of slopes other than those that are vertical or horizontal will appear different from the actual slopes. At times, exaggeration is desirable, such as in construction of a profile across a continent. (If the vertical scale were not enlarged on such a profile, then the profile would be no more than a line with a few minor wiggles). If the vertical scale is different from the horizontal scale, the vertical exaggeration should be determined and stated on the profile. An example of vertical exaggeration versus no vertical exaggeration is shown in Figure 1-7. Profile A is 10X vertical exaggeration and profile B is 5X vertical exaggeration while profile C is no vertical exaggeration.

Figure 1-7 Vertical Exaggeration (modified from Laboratory Manual for Physical Geology by Jones and Jones, 2003)

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1.3 Map Reference Systems The primary purpose of creating a topographic map is to generally record the position of topographic features of the Earth’s surface (hills, streams, lakes, etc.), along with its cultural features (buildings, streets, towers, …). However, the position of such features can also be recorded numerically using the coordinate and grid systems, and these are very efficient means to report and share location information. Both coordinate and grid systems are used to define points in space on a particular surface using distances and/or angles. Grids differ from coordinate systems in that they are usually plane-rectangular and composed of only a finite number of lines. There are several different map reference systems used and depicted on topographic maps. We will focus on two of these that appear on Canadian Topographic maps: Universal Transverse Mercator System and National Topographic System. Universal Transverse Mercator System (UTM) In the UTM system the globe is divided into 60 zones of 6° each. Each 6° zone is then “flattened” or projected onto a two dimensional plane (this causes minor geographic distortion). In Canada there are sixteen zones (7 to 22) numbered from west to east (Figure 1-9). Further reference of geographic features is then given by means of a superimposed rectangular grid. Geographic maps of Canada all have a grid (in blue) of undistorted straight lines drawn on the 60 strip after it has been flattened. Horizontal and vertical lines are drawn 1000 metres apart. Vertical lines are parallel to the central meridian in each zone. Therefore, grid north is never exactly true north (except at the central meridian, but it is very close). Notice in Figure 1-8 that the blue UTM grid is not perfectly parallel with the map edges that are aligned to ‘true’ north. This is where ‘grid’ north comes into play. The margin of each topographic map gives the zone number and the spacing of the grid lines (for example, a 1:50,000 map has grid lines 1000m apart). Usually, the zone number is given first. A number referring to the distance east of the nearest grid line west is given next, followed immediately by a number giving the distance north of the nearest grid line south. These numbers are called “eastings” and “northings” and allow the location of a point, whether named or unnamed, as precisely as the scale of the map permits (Figure 1-8).

Figure 1-8 Topographic Map showing UTM grid and reference coordinates

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Note: By convention, UTM coordinates are written in following order: Zone, Easting, Northing

Figure 1-9 UTM Zones of Canada (Courtesy of www.tbs-sct.gc.ca)

National Topographic Systems (NTS) The major reference system used in Canada is the National Topographic System (NTS). By this system, Canada is divided into numbered primary quadrangles, each 4° latitude by 8° longitude. The primary quadrangles are defined with a number and are 1:1 000 000 scale. Typically the primary is divided into 16 smaller areas. Each of the 16 areas is labeled with letters A through P. The lettering begins in the southeast (lower right hand) corner and zigzag to the northeast (upper right hand) corner. The letter is the second element in an NTS number for a map at 1:250 000 scale. Finally, the lettered quadrants are broken into 16 areas and labeled 1 through 16. These maps are at a scale of 1:50 000 and are the final part of an NTS map number. When you get to the northern areas of the NTS (above 80˚ latitude), the grid systems changes its proportions to accommodate enclosing longitudinal lines. The NTS system will not precisely locate a point. It is for map cataloguing only. The Universal Transverse Mercator (UTM) system locates points precisely using only numbers, thus eliminating the necessity for number/letter location methods. NOTE: Standard Canadian topographic maps have colour coded map reference systems to avoid confusion. For example, the Banff map sheet we will use in this week’s lab exercises has the UTM grid in light blue, the latitude-longitude system appears in black, and contour lines appear in light brown. When looking at the information on the margins of the map sheet, you’ll find information relating each system written in the corresponding colour to the system (i.e. UTM text will be in light blue).

GLGY 377 - Lab 1: Topographic and Contour Mapping Concepts

Figure 1-10 NTS Map breakdown for 93 F/12 (Marilla, British Columbia) (from: www.gis.unbc.ca and www.maptown.com)

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