In the Footsteps of the Topographic Engineers at Gettysburg

Read Part 1

Part 2: Historians and the National Park Service commemorate the Civil War’s 150th anniversary with a massive facelift made possible by modern geospatial experts.
By Curt Musselman

The National Park Service (NPS) was created in 1916, when the early parks, such as Yellowstone and Yosemite, were established primarily to protect and preserve the exceptional scenery and natural lands that were within their boundaries. In 1933, the NPS and the United States Department of the Interior took over administration of the Gettysburg National Military Park from the War Department, which had overseen the park for the previous 38 years. With the addition of Gettysburg National Military Park and a whole host of other War Department battlefields and historic sites, the NPS began to expand its expertise in the area of cultural landscape preservation.

Cultural parks such as Gettysburg are established to preserve, protect, commemorate, and interpret important events and people who made a significant contribution to the story of our nation. As such, preservation and rehabilitation of the historic landscape that witnessed and helped shape the events at Gettysburg are an important part of the NPS mission. Indeed, even the first organization to promote preservation of the Gettysburg battlefield, the Gettysburg Battlefield Memorial Association, had as part of its stated purpose, “to hold and preserve the battle-grounds of Gettysburg with the natural and artificial defenses, as they were at the time of said battle to commemorate the heroic deeds, the struggles, and the triumphs of their brave defenders.” 

Battlefield Rehabilitation

Throughout the 19th century and into the early 20th, the battlefield lands at Gettysburg continued to be farmed by subsistence farmers much as they had been prior to the battle. The efforts of the park’s caretakers—whether the Gettysburg National Park Commission (GNPC), the War Department, or the National Park Service—were primarily focused on the commemorative memorials and avenues that had been established along the lines of battle of the two armies. Only a few portions of the park’s landscape were singled out for rehabilitation work, such as the sweeping vista from Little Round Top that required frequent, periodic clearing of woody vegetation to keep the historic views open.

With the increasing popularity of Gettysburg as a tourist destination, portions of the battlefield became developed for services such as restaurants, motels, and museums. The natural growth of Gettysburg, the county seat of Adams County, Pennsylvania, also placed development pressures on the fields at Gettysburg. Park managers recognized that the historic integrity of the battlefield was being lost, so the National Park Service acquired dozens of properties and moved or demolished the buildings that had been added since 1863.

The National Park Service regularly rehabilitates designed and natural landscapes, but rehabilitation of a battle landscape is not an easy task. The overall philosophy guiding the rehabilitation work at Gettysburg is included in the park’s General Management Plan (GMP), written in 1999. The park’s GIS was used extensively in the preparation of the GMP, especially in the documentation of conditions for the entire 6,000-acre park as of 1993, 1927, 1895, and 1863.

Battlefield landscape changes were then analyzed for both large-scale features (woods, fields, orchards, and roads) and small-scale features (fences, lanes, and individual trees). The significance of key landscape features was also analyzed based on both the level of battle action and the importance of the landscape feature from a military point of view. After public review, comments, and many revisions, the GMP presented a preferred alternative for managing the park that called for the rehabilitation of much of the battlefield to its condition as of July 1863.

Using Old Documents

Documentation of the 1863 conditions for the GMP relied primarily on the Warren Map drawn in 1868 (see part 1 of this series in the December 2011 issue for more on the Warren Map). But before the park’s resource management division implemented any of the proposed rehabilitation actions (that included adding trees, removing woods, planting orchards, adding thickets, and building fences), detailed cultural landscape studies were undertaken. These studies used all possible sources of information, including maps, photographs, reports, and letters, to determine absolutely what the battlefield looked like in July 1863. Figure 2 shows 1863-era photographs (taken on Cemetery Hill looking east towards Culp’s Hill) used in this effort. Park historians use the 1:2400 scale Warren Map traced by the GNPC as the compilation base for this project, and every field and every fence line is given a name that serves as a reference to the feature’s documentation. This process provides a complete accounting of the battlefield’s 1863 features, but the park’s GIS is used to provide the final piece of information needed for rehabilitation: the exact location of the features in the field.

Using Modern Tools

The Gettysburg National Military Park has used GIS since the mid 1990s for planning, preparing archeological and cultural feature inventories, managing facilities and incidents, and studying the impact of white-tailed deer. The primary GIS computer in use is a Dell Precision T7500 desktop with dual processors, 4 GB of RAM running Windows 7 and having direct harddrive storage of 1.5 TB. The primary software includes Esri’s ArcGIS 10.0 and Trimble’s Pathfinder Office 5.0. Output from the GIS is printed on either a Canon Pro 9000 desktop printer (B format) or an HP Designjet T1120 printer (44-inches wide). The HP Designjet incorporates a T1120 SD-MFP scanner that is used to scan wide-format color materials at up to 9600 dpi. Field data is collected using a Trimble GeoXH GPS receiver, a Tornado antenna, a Geobeacon for real-time corrections, and Terrasync software version 4.13.The first GIS base maps used by the Gettysburg National Military Park were acquired by contract from photogrammetric engineers in 1993. They showed contours using a five-foot interval and were accurate to a scale of 1:7200. In subsequent years, base maps accurate to a scale of 1:4800, covering the entirety of the park, have been developed by Adams County.

In addition, every three years since 2003, Pennsylvania’s Department of Conservation and Natural Resources (DCNR) Bureau of Topographic and Geologic Survey has made available digital orthophotos at that same scale. A recent lidar mission flown by DCNR has resulted in two-foot contours for the entire park. In order to support the first two phases of the park’s landscape rehabilitation project, the park acquired new base mapping of existing conditions at a scale of 1:600 and containing one-foot contours. This piecemeal, large-scale mapping of the park has not yet been completed, but the available 1:4800-scale base mapping supplemented by more accurate GPS measurements has been sufficient for landscape rehabilitation purposes.

The Process

Numerous identifiable features from the 1863 battlefield survive in the park and are documented in the Warren Map of 1868 and the GNPC engineer’s maps circa 1900. The park uses these 1863 features, which include lines of earthworks, lunettes, stone wall intersections, and building corners to establish control points for registering and georeferencing the historic base maps that guide our landscape-rehabilitation activities. Not all of these control points are needed to perform the map registration, so there are enough of them, especially combined with the property corner stones set by the GNPC engineers, to provide us with feedback and confidence in the locations that we derive from the historic maps for replacing missing features from the 1863 landscape. The locations of the control points are captured with the Trimble GeoXH using procedures that result in points that are accurate to within two feet. Once the historic maps have been georeferenced, we identify the landscape features that require treatment and then digitize their location and add attributes describing them in ArcGIS. Next, we import the 1863 features into Pathfinder Office where we transfer the data file or background file over to the handheld GeoXH GPS unit. Within the last year, we have started to transfer the entire scanned, corrected historic map image for the area being treated because the equipment has become much more efficient at handling large image files.

We then navigate to the location of the missing 1863 feature such as a fence line, an orchard boundary, or a woodlot edge using the GeoXH’s map display. The GeoXH is used with the Geobeacon to provide us with real-time differential correction, which is essential when we are performing layout. We then place a pin flag in the ground once we have carefully zoomed in enough on the map display so that a small step to the left or right moves the cursor (indicating the GPS unit’s position) across the line that represents the 1863 feature. Figure 3 shows the GeoXH display with an historic conditions map image of Powers Hill and lines representing the treatment area boundaries.

Maintaining Landscapes with 3D Models

The demolition of the National Tower overlooking the Gettysburg Battlefield on July 3, 2000 inaugurated the landscape rehabilitation project at Gettysburg. Since then, the park has planted 48 acres of woods, replaced 14 miles of missing fences, planted 25 acres of historic thickets, added 118 acres of historic orchards, and opened up 346 acres of overgrown or wooded fields. All of this was accomplished using the best tools and techniques available for historic map study and analysis. Even though the resource management division’s emphasis has shifted to maintenance and sustaining the historic landscapes, there are still 25 miles of fence lines to lay out and build and 133 acres of overgrown fields and fence lines to be opened up.As the landscape rehabilitation work progresses, the park continues to improve the quality of the data it is using and to upgrade its tools and procedures. Using the 3D Analyst tools in ArcGIS, the park has created a 3D model of the battlefield using precise elevations from lidar data captured by the Pennsylvania Bureau of Topographic and Geologic Survey. An earlier 3D model created in 1996 was used in support of the General Management Plan. Figure 4 of the GMP, Key Viewsheds, shows the degrees to which various areas in the vicinity of Gettysburg are visible from a series of key observation points within the park. Since that time, we have used the ability to create viewsheds (delineations of what can be seen from where) to help analyze the impact of activities such as the construction of buildings and cell towers and the rehabilitation of thickets and fields present in 1863.

Figure 1 on the first two pages of this article shows output from the 3D model that the park uses to help plan and implement the landscape rehabilitation project. A few locations are labeled for orientation in this bird’s-eye view that looks northward over the Peach Orchard toward the Borough of Gettysburg. This model was built with ArcScene software that is part of Esri’s ArcGIS. Elevations have been exaggerated for effect in this rendering, which also shows in 3D (extruded to their approximate height) some of the features of the battlefield in 1863. Orchards are shown in orange, woods are green, fence lines are yellow, and buildings are dark gray. Modern roads are shown by black lines.

The ArcScene tools also enable the creation of fly-throughs of the terrain from any altitude or point of view, and the fly-throughs can then be recorded into video animations. The software can also be used to create and capture static views of any part of the park from almost any angle. Such products help give park management and the public an idea of what the battlefield will look like in the next 10 years when rehabilitation of the cultural landscapes to their 1863 appearance is completed.

Although the rehabilitation project is controversial or unpopular with people who are uncomfortable with the NPS cutting down trees within a park, the project is realistically an unparalleled success. After decades of benign neglect under early NPS administrators, where fields that had been open since the time of the battle were allowed to grow closed, the park is starting to look more like the battlefield that the park’s creation was intended to preserve.

Historians and visitors alike can now appreciate the life-and-death importance of the fields of fire and avenues of approach that were so significant to the troops who fought here. And, after years of making measurements in the field, pouring over the historic maps, and literally following in the footsteps of the topographic engineers, we are now able to see what the topographic engineers saw in 1868 to a greater degree than at any time within the last 50 years.

Visit our website or YouTube channel for videos of Curt talking about his work on location and our Flickr account for photos of Gettysburg National Park.

CURT MUSSELMAN is a native of Gettysburg, PA and is the National Park Service Cartographer at the Gettysburg National Military Park. He has a BA in history from Bucknell University and an MS in cartography from the University of Wisconsin-Madison. He has also worked as a licensed battlefield guide at Gettysburg and as a quality assurance program manager at Esri.

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