The Mississippi River has evolved throughout its history as the river channel has meandered back and forth across the landscape of the central U.S. These are usually included in the map legend. Figure 9.1 – Common map symbols used on geologic maps. Figure 9.1 shows the common symbols used for geologic structures. Look at the tables in Chapter 2 Earth Materials to see some common patterns for different rock lithologies. Again, there are often standard colors for different ages of rocks and patterns for the rock types. Most geologic maps will have a stratigraphic column with either colors or patterns to distinguish various rock units. If you didn’t learn about strike and dip in Physical Geology, now is the time to do so. You also need to be able to read strike and dip symbols. What do you need to know for geologic maps? First, there are lots of standard symbols used to help geologists worldwide use the same terminology. Is there a publication or guidebook associated with this map? The year the map was released or revised. What is the source of the geographic information? For example, is it based on a USGS topographic map, or is it a satellite image? What is the map projection? Selected reference locations or features such as a town, river, state boundary, mountain, etc.Ī list of authors, compilers, editors, publishers, associated publications (text or guidebook), URL, and any other information so it can be accurately cited in reference list or bibliography. Most maps also have a visual scale bar of relative distance on the map.Īn arrow pointing north and, if possible, latitude and longitudeĮxplanation of any symbols used on the map, including colors, lines, or icons. The scale should be relative to both kilometers and miles. The ratio of distance on the map and distance on the ground. Table 9.1 – Common map information InformationĬoncise information related to geographic information and map contents Below is a list of information typically associated with maps. Also, the lines between the different colors represent contacts between different rock types.īefore interpreting or preparing a map, it is important to understand some of the background information about the map. In previous chapters, you have seen how colors and patterns can be used on maps to distinguish different types of rocks, such as volcanic (orangish) versus plutonic (red) in Figure 2.24. Anything that has a visual distribution can be mapped. Mapping is also used in astronomy (planet and moons, regions of space, etc.). Maps may represent the surface of the land or areas in and around lakes and oceans, the seafloor, or features known or thought to occur underground. It can be challenging for someone unfamiliar with these features to look at a geologic map and visualize reality. This is one of the great difficulties in geology because geologic maps represent 3-dimensional features in a 2-dimensional format. Some maps even attempt to portray 3-dimensional landscape features, such as mountains or canyons. Maps are a scaled, 2-dimensional representation of the surface of an area. If you have used a mapping app to get directions somewhere, you have used a map. In the past, you probably encountered a variety of types of maps. 9.1 Introductionĭo you remember in Chapter 0 how we said you would become an expert at reading and interpreting geologic maps? Now is the time to sharpen this skill. Some of the maps in this chapter can be printed on poster paper from large PDF files found here (opens in a new tab). Identify geologic structures on a geologic map.Visualize geologic structures in maps and cross-sections.
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