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Ã Students measuring elevations in a model map area. Provenance: Lynne Elkins, Bryn Mawr College Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license. This exercise was designed in a department that has some basic support for developing inexpensive classroom equipment in cooperation with a machine shop. The shop built gridded mapping frames to my specifications using a simple aluminum design (a square frame of aluminum with small pins inserted at one-inch intervals). An even simpler DIY design could use thin but sturdy pieces of wood to create a wooden frame, with steel nails. My initial design called for 2'x2' frames, which turned out to be too large: mapping a 4 sq. ft. space at 1-inch resolution took more than a standard lab period for most students to complete. The attached exercise instructs students to use a smaller portion of the mapping grid; this can be revised for different size grids. Another issue to be aware of when designing mapping grid frames is whether to label the spaces with letters and numbers (as is done on many maps and was thus my original thinking) or to label the lines between the spaces, which is easier for data collection. At the start of the lab, I typically give my students a few ground rules: they should avoid extremely flat areas, because the elevation rounding they are likely to do will make contouring them very difficult; their highest point should be at least 2 inches and not more than 4-5 inches high; they may not have vertical walls or overhangs (and should really keep the slopes less than 60-70Â at their steepest); the table surface is sea level with zero elevation; and most of their model area must be mappable land (not ocean, i.e. bare table). I give them large sheets of wax paper to construct the model on, for easy cleanup. I also provide large sheets of 1" grid paper so they can create a 1:1 map of their model (and I impose a scale calculation later for the model), and remind them several times not to invert the map labels when setting up their map grid. Typically this is all they need to know to begin creating and mapping a landscape. The mapping tools are pieces of string (to string across the pins on the mapping frames and position the grid points) and wooden skewers labeled with quarter-inch markings. After an initial attempt to make the playdough for this lab, my department opted to purchase 6-lb. tubs of commercial playdough. It is ultimately relatively inexpensive because it is reusable almost indefinitely, as long as it is stored tightly sealed (we use zip-loc bags inside the commercial containers) and occasionally spritzed with water--once a year usually works fine for keeping it hydrated for storage over the rest of the year, but that may vary with climate and frequency of use. Typically I walk around while they are getting started and make commentary on their landscapes, and then when there are no further questions I go to the board and create an example data set and contour map. While a photocopied paper example map would accomplish the same thing, this approach lets me tailor my examples to what I see they are doing (e.g., including circular depressions, saddles, or ridges). I also have handy and frequently refer the students to USGS quads from around the country when they are mapping, e.g. a very flat quad with depressions in central Florida and a very steep quad from the Grand Canyon. When they are mapping, I typically advise them to 1) sketch in the shoreline around their zero-elevation values by comparing to the model, 2) add major peaks between grid lines as needed, and 3) map from the highest parts of their map area downward. I also discourage contour intervals smaller than 1/2-inch, particularly when their model contains flat terrain. Many students want to be more precise, and if they have estimated depths to the nearest 1/8-inch it is possible to contour at 1/4-inch intervals, but typically their rounded measurements in flat areas make this quite tricky. It often is necessary for me (and/or TAs) to walk around and give them advice in places they are stuck and remind them how contours work. Making the profile is usually very quick. The graph provided would need to be adjusted/replaced for different size mapping grids, but works well for a grid that runs from A to O on one side and from 1 to 10+ on the other. If they are kept on task everyone except the most cautious or disorganized groups can typically finish elevation measurements for about 2 sq. ft. of map area within 1.5 hours. With an introductory spiel, that leaves about an hour for finishing most of the contouring and transferring data for the profile. Faster groups will probably finish all the final details but are well-advised to take the lab home to double check the details. Slower groups may finish coloring and looking at the local topo map on their own. Longer lab periods would permit a more detailed study of the local USGS maps and/or a larger model size--this was written for a 3-hour lab period.
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