Lab 2

Goal and Background

          The main purpose of Lab 2 was to familiarize with georeferencing and digitizing techniques from GIS I in order to solve spatial referencing problems and analyze spatial data in preparation or new concepts in GIS II.

Methods

          Open ArcMap and set up the georeferencing toolbar from the Customize tab. Bring the Centerlines_clip shapefile into ArcMap so that the data frame projects on the fly for that projection. Then add the Topographic base map from ESRI. Next, bring in the scanned 1878 map of Eau Claire, WI which will be georeferenced to the Centerlines_clip as its reference. Using the georeferencing toolbar, Fit to Display the scanned map and shift and scale the map so that it relatively matches the base map. Adding transparency to the scanned map will make this process easier. Add control points by clicking the scanned map first and then to its corresponding place in the reference image or feature class. Control points should be equally dispersed across the target image, but in this case, that might not be entirely possible. Easily distinguishable features between the target and reference image were clustered around the center of the image. Add control points until the scanned map lines up with the reference image until it is satisfactory. The RMS might be high, but considering the 140-year gap between the reference and target image, if it visibly looks alright, it'll have to do. Set a transformation. A first-order transformation might be the most appropriate choice since the warping of the other orders aren't necessary for a scanned map and the exact coordinates aren't known for a spline transformation (if there's enough control points). Update georeferencing when finished. Set the transparency to 50% to inspect how well the georeferenced image fits the base map (Figure 1).

          The second part of the lab involving creating data to analyze the differences in water area between 1878 and 2018. First, create a new geodatabase. From the Toolbox, open the Create Feature Class tool. Set its location to the new geodatabase, name it hydro_1878, set its geometry type to polygon, and set its coordinate system to the same one as Centerlines_clip. Bring in the study area shapefile into the data frame. Open the Editor toolbar and click Start Editing. Edit the feature class hydro_1878. Using polygons, digitize the Chippewa River, Eau Claire River, and Half Moon Lake within the study area using the georeferenced 1878 scanned map as a reference. Save edits and click Stop Editing. Now create another feature class and call it hydro_2018. Start editing the hydro_2018 feature class. Digitize the Chippewa River, Eau Claire River, and Half Moon Lake within the study area using the ESRI Topographic base map as a reference. Save edits and stop editing. Open the new feature classes' attribute table and use Statistics on the Shape_Area field to compare the total area of water between 1878 and 2018. Visually compare the differences by displaying the feature classes together (Figure 2).

Results

          Figure 1 shows the 1878 scanned map georeference and displayed with a 50% transparency over a topographic base map. 

Figure 1: Map of the 1878 Eau Claire map georeferenced over a modern base map.

          Figure 2 shows the differences between water features in 1878 and 2018. Visually, there appears to be more water area in 2018, but in reality, there was more water area in 1878, given by the statistics in the attribute table.

Figure 2: Map of the water area differences in Eau Claire, WI between 1878 and 2018.

Sources

David Ramsey Map Collection (2018). Eau Claire and Medford. Retrieved  from https://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~4181~480085#.

Eau Claire County (2014) Master_Centerlines. Retrieved from Caitlyn Curtis.

ESRI (2018). Wold Topographic Map. Retrieved from https://www.arcgis.com/home/item.html?id=30e5fe3149c34df1ba922e6f5bbf808f.