Maps are essential tools. Maps are as important in geology as written texts are in the study of literature. By studying maps, a geologist can see the shape and geology of the earth’s surface and deduce the geological structures that lie hidden beneath the surface.
It takes some training to read maps skillfully. Geologists are trained in map reading and map making. Many geologists have experience mapping some part of the earth’s surface.You are not expected to become a geological expert in reading maps. However, you will be expected to develop your map reading skills as you maps to help you learn the geology of a given area.
A geological map needs:
A series of polygonal shapes representing the distribution of various rock types across Earth's surface; dark and light shading or stipple may be used to indicate areas of rock outcrop vs extrapolation
A compact legend that succintly explains the nature of the various rocks units, with the units ordered by age (youngest at the top)
An informative title, the identity of the creator(s), and a date or creation/publication
A scale and north arrow
Annotations that indicate faults and the strike and dip of bedding and/or folia; symbols should be explained in the legend
An interpretative cross-section, usually drawn as a vertical plane, that illustrates the 3D relationships of the rock units; the start and end of the section line will be indicated on the map
A general diagram that provides context of the map location, such as the location in a geographic state or county
https://wiki.aapg.org/Geologic_mapping_(UB)#How_To_Read_Geological_Maps
After: https://commons.wvc.edu/rdawes/basics/mapkey.html
Topographic maps are a basic tool for hikers, planners who make decisions on zoning and construction permits, government agencies involved in land use planning and hazard assessments, and civil engineers. They portray grids that are used on deeds to identify the location of real estate, so homeowners and property owners often find it useful to refer to topographic maps of their area.
Topographic maps represent the three-dimensional shape of the land. Most topographic maps make use of contour lines to depict elevations above sea level. Contour lines reveal the shape of the land in the vertical direction, allowing the 3-dimensional shape of the land to be portrayed on a 2-dimensional map. When you know how to read contour lines, you can look at a topographic map and visualize the mountains, plains, ridges, or valleys that it portrays. Such topography can reveal provide information about the geology beneath the surface. Earth’s landforms result from surface processes such as erosion or sedimentation combined with internal geological processes such as magma rising to create a volcano or a ridge of bedrock being pushed up along a fault. By studying the shape of the earth’s surface through topographic maps, geologists can understand the nature of surface processes in a given area, including zones of erosion, zones subjected to landslides, and zones of sediment accumulation. They can also find clues to the underlying geologic structure and geologic history of the area.
On a topographic map, a contour line is a line of constant elevation. For example, every point on a 100 m contour line represents a point on earth that is 100 m above sea level. Contour lines never intersect as a point on Earth's surface cannot be at two different elevations. A constant specified vertical distance called the contour interval separates each contour line from adjacent contour lines. A commonly used contour interval is 10 or 20 m. On a map with a 10 m contour interval, the elevation difference between two contour lines that are next to each other is 10 m, regardless of the physical distance between the two lines on the map. Contour lines curve up stream when they cross a valley (and down hill as they cross ridges). Where contours are close together, the topography is steep; where they are far apart, the slopes are gentle.
A geologic map shows mappable rock units, mappable sediment units that cover up the rocks, and geologic structures such as faults and folds. A mappable unit of rock or sediment is one that a geologist can consistently recognize, trace across a landscape, and describe so that other people are able to recognize it and verify its presence and identity. Mappable units are shown as different colors or patterns on a base map of the geographic area.
Second, geologic maps are essential tools for many practical applications as the present fundamental scientific information to assist decision making in zoning, civil engineering, and hazard assessment. Geologic maps are also vital in finding and developing geological resources, such as gravel to help build the road you drive on, oil to power the car you travel in, or aluminum to build the more fuel-efficient engine in your next vehicle. Another resource that is developed on the basis of geologic maps is groundwater, which many cities, farms, and factories rely on for the water they use.