Lab 2: Georeferencing and Data Creation

Goals and background
The purpose of this lab was to give students a review of georeferencing skills as well as digitizing and creating new feature classes.  This was done through georeferencing a city map of Eau Claire from 1878 and comparing it to a current map to visualize the change in water features over the last 140 years.

Methods 
The first part of this lab requires students to georeference an 1878 map of Eau Claire (shown in figure 1) and a 2018 map by using the georeferencing toolbar provided in ArcMap.  The old map is aligned to the current map by adding ground control points in the middle of street intersections.  The aim was to get the EMS error as low as possible, managing to bring it to approximately 1.36 with 29 GCPs as shown in figure 2.

Figure 1: 1878 map of the city of Eau Claire

Figure 2: A list of ground control points as well as the total RMS error

Part two of the lab had students create a feature class, digitizing polygons within it. All of the major water features in the 1878 image were to be digitized within the study area.  The same process was done for the 2018 map of Eau Claire.  This was conducted by utilizing the editor tool and selecting "create polygons". 

Results
Figure 3 below displays a georeferenced map of Eau Claire placed over a current map.  The river between 1878 and now do not completely line up, but georeferencing them still did an impressive job with overall alignment. 

Figure 3: A georeferenced map of Eau Claire (1878-2018)

Figure 4 below shows a map of the two water features.   As you can observe, the river is generally more narrow now than it was 140 years ago.  The difference in the amount of water in the study area is over 1,000,000 square feet less than what it was in the 1878 map. 

Figure 4: A comparison map of water features from 1878-2018

Sources
1. David Rumsey Map Collection https://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~4181~480085#

2. Master_Centerlines feature class (clipped), Eau Claire County

3. World Topographic Map, ESRI, 2018: https://www.arcgis.com/home/item.html?id=30e5fe3149c34df1ba922e6f5bbf808f