Excerpts from Teaching v Documents: Using major Sources indigenous the national Archives National Archives and Records administration and national Council for the society Studies Washington, D.C. 1989
Maps using Hachure and Contour Methods
Map makers have traditionally supplied various means to represent the three dimensions that the planet in two-dimensional images. Prior to the nineteenth century, because that example, the many common machine for denote relief on a map was v variations of light and shade.
You are watching: Hachured contour lines on a topographic map represent
As the use of shading ended up being systematized during the eighteenth and also nineteenth centuries, French cartographers described these shading lines together \"hachures.\" Hachures stand for the steep of the landthe much more gentle the slope, the under the linesand the lack of heat indicates level terrain. The illustration on the right side of the paper is an example of this system.
The usage of edge lines to visually represent different elevations the land come into basic use towards the end of the nineteenth century. Very early version of a edge map is checked out on the left. Merely speaking, a solitary contour line corresponds to a single elevation that the land. Since the edge line defines a curved surface ar (the earth), every line encloses a an ext or less circular area. The complete effect is a sample of concentric lines. The \"base\" heat or datum for most contour maps is sea level, v each heat on the map representing a conventional distance over or below the base line. As each line signifies rise or decrease in the land elevation (in this map, 3 feet), one can accurately calculate height by merely counting the lines indigenous the base line (the water\"s edge in this instance). The slope of any readjust in the see relief can additionally be figured out by noting the proximity that the edge lines to one another. A high concentration that lines tells the map user that the elevation alters sharply, while commonly spaced lines indicate a gradual slope.
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The 2 maps the Salem Neck, Massachusetts, surveyed by George W. Whistler (father of artist James A. McNeill Whistler) and also William G. McNeill, topographical designers for the United states Army, were created for a study carried out in 1822 the fortifications in the area. Once the Office of cook of Engineers decided in 1861 to examine the feasibility of reconditioning the forts, they described these maps and also the reports accompanying them.
This document is part of the records of the Office the the chief of Engineers, united States army (Record group 77, Fortifications file, drawer 18, paper 11).
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Suggestions because that Teaching
In order because that students to answer the following questions, they need to (a) research the maps closely, (b) familiarize themselves with the scale and also accompanying keep in mind (located in ~ the bottom center of the document), and (c) recognize contour and also hachure approaches of mapping. (The exercises can be adjusted to fulfill the needs of your students.)
Maps as MapsBasic Map Skills:
1. What proof is over there in this paper that tells you the the land area is not an island?
2. What descriptive information included in the map top top the right side of the illustration is omitted on the left?
3. Calculate the length and width of Salem Neck in miles.
4. Just how are points of elevation represented on each of this maps?
5. Using both maps, shot to calculate the elevation of the area where the Alms house is located. I m sorry of the 2 maps is preferable? Why?
Maps as historic Documents:
1. What go this document tell you about mapping techniques in 1822?
2. Is there proof in the record that the map was used after 1822?
3. How can this document have been valuable to chroniclers and/or cartographers in the past? How and why might it be offered today?