Employees in the News. Emergency Management. Survey Manual. As one of the cornerstones of the U. It has many uses ranging from recreation to scientific analysis to emergency response.
It uses easy to navigate foundational base maps and makes it simple to interact with all our data themes to create your own map.
The National Map is a suite of products and services that provide access to base geospatial information to describe the landscape of the United States and its territories. The National Map embodies 11 primary products and services and numerous applications and ancillary services.
The National Map supports data download, digital and print versions of topographic maps, geospatial data services, and online viewing. Customers can use geospatial data and maps to enhance their recreational experience, make life-saving decisions, support scientific missions, and for countless other activities.
Nationally consistent geospatial data from The National Map enable better policy and land management decisions and the effective enforcement of regulatory responsibilities. The National Map is easily accessible for display on the Web through such products as topographic maps and services and as downloadable data. The geographic information available from The National Map includes boundaries, elevation, geographic names, hydrography, land cover, orthoimagery, structures, and transportation.
The majority of The National Map effort is devoted to acquiring and integrating medium-scale nominally , scale geospatial data for the eight base layers from a variety of sources and providing access to the resulting seamless coverages of geospatial data. Professional geologists use exercises such as the ones you will practice with below to help you and us visualize a two dimensional cross-section of what the land surface looks like from the side - giving you a slice of the third dimension.
In other words, profiles help you to understand what a topographic map is telling us about hills and valleys along a particular line. Examine the topographic map image to the left you can click on the image to make it larger or you can download the map and a profile Acrobat PDF 2. Before you start, you might want to review some of the rules about topographic maps before continuing you can find rules at Idaho State U. To construct a topographic profile, you need to find a line on a map that is interesting.
In many cases, this line is given to you often labeled something like A-A' or A-B. The line should go through some part of the map that you are interested in, so that you get useful information. The following list provides some guidelines for effectively constructing a topographic profile and uses the topographic map and profile line provided to the left you can download a pdf of the map and profile to work from Acrobat PDF 2.
Show me the line on this map. Show me how to line up the paper. For this profile, we've used the profile line provided and lined it up with the profile line on the map. Any blank piece of paper will do but sometimes it's just easier to use the graph paper. We've lined up the bottom of the graph paper with the profile line and marked each end with A and A'.
Show me how to mark the paper for this problem. Now that we have the paper lined up, all we have to do is make a mark and label it everytime we see a contour line cross the profile line. The image below has all of the contour lines marked with blue tick marks and most of the contour lines are labeled except where they get really messy.
Show me the highest and lowest elevation for this problem. The highest elevation recorded on the profile is ft and the lowest is ft.
This will become important when you need to begin to plot your profile. Show me how to do this for this problem. As stated above, we have an appropriate profile graph for this problem this will likely be true if you have a lab manual from a national publisher. You can see how to mark the graph paper in step 3 if you aren't sure how to do this step. Show me how to label my profile line. We've already labeled the x axis with A-A'. In step 4, we determined the is the highest elevation and is the lowest.
You have plenty of horizontal lines and since the contour interval is 20 ft, let's start with ft and make each line 20 feet higher. Label each mark with the elevation of the contour it represents. Prepare a vertical scale on profile paper by labeling the horizontal lines corresponding to the elevation of each index contour line. Place the paper with the labeled contour lines at the bottom of the profile paper and project each contour to the horizontal line of the same elevation.
Connect the points. Stream Gradient: Stream gradient can also be determined from a topographic map. The gradient of a steam or river is determined by measuring a section of a stream or river and dividing the distance in miles into the vertical difference in feet between the two points. The result is expressed in feet per mile ft. The equation used is:.
Tips for Interpreting Topographic Maps Vertical exaggeration : Vertical exaggeration is the effect that is created when the horizontal and vertical scales on your topographic profile are not the same. Determining hillslope : Among other things, a topographic map can be used to measure the average slope of a hill or hills. Topographic Map Example As an example, look at a map of the Sulphur-Boundary Creek area along the Middle Fork of the Salmon River This map is a geologic map of glacial geology in the area, drawn on a topographic map base.
The map has a contour interval of forty feet, which means that every place between the marked foot line and the next lowest line which is feet, and not marked has an elevation equal or greater than feet, but less than feet.
You can figure out the elevation of any point by finding the nearest labeled line, counting the number of lines above or below it, multiplying by the contour interval, and adding or subtracting the result from the nearest marked contour line.
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