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CHAPTER 3 : MAP READING AND INTERPRETATION PURPOSE: EVERYBODY KNOWS HOW TO READ A MAP, WHY DO WE NEED TO DO THIS? When you set up a field experiment, it is essential to know how to get as much detailed information as possible. You need to know how to: 1) find and recognize a sampling site, 2) determine the easiest route to the site, 3) recognize high and low areas to determine water flow direction, 4) measure distance to be traveled, not just in a straight line, but up and down hills and around corners, and 5) describe, by simple means, the location of special features on a site. WHAT TYPE OF MAP SHOULD WE USE? There are a wide variety of maps such as political, statistical, or simply geographical; each has its own purpose. We are going to use a 7 1/2 minute Topographic map or Quadrangle . Why is this map called a 7 1/2 minute series? (Hint: Look at the latitude and longitude designations at the four corners of the map) The physical features of an area, whether natural or cultural, are called its topography. A topographic map shows relief (ups and downs). HOW DO I LOCATE POTENTIAL SAMPLE SITES ON A MAP? Topographical maps show physical features such as hills, ridges, valleys, streams, lakes, marshes, woods and peaks. They also show cultural features (man-made features) such as roads, trails, railroads, bridges, towns, cities, buildings, and fences. Topographic maps also provide vertical information through the use of contour lines (Figure 3-1). All points on any one contour line have the same elevation above sea level. Every contour closes on itself and encloses an area either within or beyond the border of the map. Contour lines never split. Contour lines will appear close together when expressing a steep slope, and widely spaced when expressing a gentle slope. Not all contour lines are labeled with an elevation; the ones that are labeled usually have a thicker line. To find out the elevation of an unmarked contour line, locate the two heavy labeled lines on either side of the unlabeled line. Then count the number of unlabeled lines in between. The unlabeled lines are always spaced equally apart with regard to change in elevation. For example, look at Figure 2-1. Chapter 1 1 Fig ure 3-1: Contour lines with and without elevation labels.
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Lines A and F are the marked contour lines (1000’ and 1200’ respectively). Assume that you want to know the elevation of line E. Since there are four unmarked lines (B-E) between the marked lines, they must be spaced 40’ apart. Therefore, the elevation of line E is 1160’ above mean sea level. HOW DO I REFERENCE AN AREA ON THE MAP? There are a variety of ways to reference areas or locations on a map. UTM (Universal Transverse Mercator) coordinates are commonly used to refer to a specific area. Latitude and longitude are used to pinpoint a location.
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