Historical Mapping: Elevation Data
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Introduction
This lesson will include numerous technical skills required to analyze a civil war battlefield. In this lesson the learner will use previously discussed concepts of digitalization and georeferencing, see the lessons on georeferencing and digitization for a more in-depth understanding. The primary purpose of this lesson is to learn technical skills such as creating TINs, Hillshade, Contour, Viewshed, and Line of Sight. The Perryville Civil War battlefield in Kentucky will be used to learn the techniques for this analysis. This battlefield was selected because it was the largest Civil War battle in the state of Kentucky and many of the western theater battlefields are less clearly understood than those in the eastern theater by the majority of the population. The techniques presented in this lesson can be used for other types of historical maps and other analyses.
Purpose
In this lesson, a historical Civil War battlefield map will be the focus, other maps and data sources will also be used to construct modern geospatial maps. The constructed maps will show elevation, troop placements, Lines of Sight, Hillshade, Slope; Viewshed mapped on today’s landscape. The learner will utilize research techniques to gather both mapping information as well as historical events that can be used to understand what happened in Perryville in October of 1862. This lesson will emulate the methods used in historical research.
Concept
- Use of basemap layers, raster and vector files
- Using DEM (Digital Elevation Models)
- Mosaic of Raster Images
- Creating Contours
- Creating Hillshade and Slopes
- Creating Lines of Sight
- Creation of TIN (Triangulated Irregular Network)
- Georeferencing of historical maps and other non-GIS maps
- Digitizing positions from georeferenced maps
Procedural Order
- Researching the particular area of interest is required. For example, if you are exploring the Perryville Civil War battlefield you first must begin your study by researching the battle and the events that lead to the conflict at this location. The events that occurred after the battle must also be understood. This understanding will allow for proper data collection to completely represent the events on the battlefield. Much of the Perryville battlefield is located in a Kentucky State Park just outside the town of Perryville.
- A base layer must be established; different base layers might be used at different zoom levels. The base layer might be an online source map or a created layer. This base layer could be a topographic map, street map or imagery. Depending on the data source more than a single image may be required.
- The next step is to locate appropriate shapefiles for items such as rivers, roads, etc. Make sure that the shapefiles are in the same projection as the base layer. Depending on the base layer selected some of the features listed, might not be required since they may be included in the base layer at an appropriate detail level for the project. In a base layer the designer does not have control over what is displayed and at what zoom level.
- Digital elevation files are required and must be downloaded for the region. Depending on the source of the data selected, the data may need to be converted from a DEM (Digital Elevation Model) into a raster to ensure that they are properly projected. The DEM files may need to be mosaiced together depending on the area being viewed (completed using ArcToolbox). This would be needed when more than one image is required to see the entire battlefield.
- Once the DEMs are in a usable format, a contour map will be created using the 3D Analyst tools in the ArcToolbox.
- From the contour map produced in step 6, other maps can be created such as a Hillshade, and Slope to assist in the analysis of the battlefield (generated using 3D Analyst).
- A TIN is created as the next step in the process, which has the appearance of a solid model surface. The shading color is completed using symbology.
- Once steps 2 through 7 have been completed, all needed base information has been established. The next step is to locate maps and images of troop positions. These can be either modern maps created from historical documentation or historical maps. Once these items have been located and downloaded, they must be georeferenced to the base layer. Once the file has been successfully georeferenced, make sure the point conversion table is saved and a layer file is created.
- The next step is digitization the georeferenced map. The referenced items might be important structures, landscape features and troop positions, to name a few. When digitizing troop positions, your file should contain the following attributes: regiment number, commander of the regiment, side which they fought for (Union or Confederate), type of troops (infantry, artillery, cavalry), information about the unit structure such as what corps, division, brigade they belonged to and time they were in that position which might include a beginning and ending time. A single regiment may be displayed multiple times as it moves during the battle. Many times, units are referred to by the name of the commander, which can be confusing if a leader is injured or killed on the battlefield.
- The next step is creating Lines of Sight and Viewshed for important locations where terrain played a significant role in the outcome of the battle. What is being established are specific locations of units and commanders to determine what was visible due to the geographic features of the terrain.
- Display historical features, such as the location of items placed on the National Registry of Historic Places. This information will be useful for those visiting the battlefield, the location of historical markers and battlefield description signs will also assist those visiting the battlefield. This type of data should be collected and created as separate layers.
- Creating a static or dynamic presentation requires gathering additional information which brings the battle to life such as pictures of leaders, current and old photographs of the battlefield, battle flags, etc. Realize that the information created and gathered might require producing multiple maps and making some layers semi-transparent.