Topographic Maps

Topographic Maps Topographic maps (often called topo maps for short) are large scale (often greater than 1:50,000) maps that show a wide range of human and physical features of the Earth. They are very detailed maps and are often produced on large sheets of paper. The First Topographic Map In the late 17th century, French finance minister Jean Baptiste Colbert hired surveyor, astronomer, and physician Jean Dominique Cassini for an ambitious project, the topographic mapping of France. He [Colbert] wanted the kind of maps that indicated man-made and natural features as determined by precise engineering surveys and measurements. They would portray the shapes and elevations of mountains, valleys, and plains; the network of streams and rivers; the location of cities, roads, political boundaries, and other works of man. (Wilford, 112) After a century of work by Cassini, his son, grandson, and great-grandson, France was the proud owner of a complete set of topographic maps the first country to have produced such a prize. Topographic Mapping of the United States Since the 1600s, topographic mapping has become an integral part of a countrys cartography. These maps remain among the most valuable maps for government and the public alike. In the United States, the U.S. Geological Survey (USGS) is responsible for topographic mapping. There are over 54,000 quadrangles (map sheets) that cover every inch of the United States. The USGS primary scale for mapping topographic maps is 1:24,000. This means that one inch on the map equals 24,000 inches on the ground, the equivalent of 2000 feet. These quadrangles are called 7.5 minute quadrangles because they show an area that is 7.5 minutes of longitude wide by 7.5 minutes of latitude high. These paper sheets are approximately 29 inches high and 22 inches wide. Isolines Topographic maps use a wide variety of symbols to represent human and physical features. Among the most striking are the topo maps display of the topography or terrain of the area. Contour lines are used to represent elevation by connecting points of equal elevation. These imaginary lines do a nice job of representing the terrain. As with all isolines, when contour lines lie close together, they represent a steep slope; lines far apart represent a gradual slope. Contour Intervals Each quadrangle uses a contour interval (the distance in elevation between contour lines) appropriate for that area. While flat areas may be mapped with a five-foot contour interval, rugged terrain may have a 25-foot or more contour interval. Through the use of contour lines, an experienced topographic map reader can easily visualize the direction of stream flow and the shape of the terrain. Colors Most topographic maps are produced at a large enough scale to show individual buildings and all streets in cities. In urbanized areas, larger and specific important buildings are represented in black though the urbanized area surrounding them is represented with a red shading. Some topographic maps also include features in purple. These quadrangles have been revised solely through aerial photographs and not by the typical field checking that is involved with the production of a topographic map. These revisions are shown in purple on the map and can represent newly urbanized areas, new roads, and even new lakes. Topographic maps also use standardized cartographic conventions to represent additional features such as the color blue for water and green for forests. Coordinates Several different coordinate systems are shown on topographic maps. In addition to latitude and longitude, the base coordinates for the map, these maps show UTM grids, township and range, and others. Source Campbell, John. Map Use and Analysis. 1991. Monmonier, Mark. How to Lie With Maps. Wilford, John Noble. Mapmakers.

Make Your Own Sugar Crystals for Rock Candy

Make Your Own Sugar Crystals for Rock Candy Its easy to grow your own sugar crystals, which are also known as rock candy because the crystallized sucrose, also known as table sugar, resembles rock crystals and you can eat your finished product. You can grow clear, beautiful sugar crystals with sugar and water or you can add food coloring to get colored crystals. Its simple, safe, and fun. Boiling water is required to dissolve the sugar, so adult supervision is recommended for this project. Difficulty: Easy Time Required: A few days to a week Rock Candy Ingredients 1 cup water3 cups table sugar (sucrose)clean glass jarpencil or butter knifestringpan or bowl for boiling water and  making the solutionspoon or stirring rod How to Grow Rock Candy Gather your materials.You might want to grow a seed crystal, a small crystal to weight your string and provide a surface for larger crystals to grow on. A seed crystal isnt necessary as long as youre using a rough string or yarn.Tie the string to a pencil or butter knife. If you have made a seed crystal, tie it to the bottom of the string. Set the pencil or knife across the top of the glass jar and make sure that the string will hang into the jar without touching its sides or bottom. However, you want the string to hang nearly to the bottom. Adjust the length of the string, if necessary.Boil the water. If you boil your water in the microwave, be very careful removing it to avoid getting splashed.Stir in the sugar, a teaspoonful at a time. Keep adding sugar until it starts to accumulate at the bottom of the container and wont dissolve even with more stirring. This means your sugar solution is saturated. If you dont use a saturated solution, then your crystals wont grow quickly. On the other hand, if you add too much sugar, new crystals will grow on the undissolved sugar and not on your string. If you want colored crystals, stir in a few drops of food coloring.Pour your solution into the clear glass jar. If you have undissolved sugar at the bottom of your container, avoid getting it in the jar.Place the pencil over the jar and allow the string to dangle into the liquid.Set the jar where it can remain undisturbed. If you like, you can set a coffee filter or paper towel over the jar to prevent dust from falling into the jar.Check on your crystals after a day. You should be able to see the beginnings of crystal growth on the string or seed crystal.Let the crystals grow until they have reached the desired size or have stopped growing. At this point, you can pull out the string and allow the crystals to dry. You can eat them or keep them.If youre having trouble growing sugar crystals, here are some special techniques and a video tutorial. Tips: Crystals will form on a cotton or wool string or yarn, but not on a nylon line. If you use a nylon line, tie a seed crystal to it to stimulate crystal growth.If youre making the crystals to eat, dont use a fishing weight to hold your string down. The toxic lead from the weight will end up in the water. Paper clips are a better choice, but still not great.