LAB 2: Georeferencing and Data Creation
LAB 2: Georeferencing and Data Creation
Goal and Background
The goal of lab two is to understand how to properly georeference data that does not contain a spacial reference. Additionally, new data will be created to help solve spatial questions.
To apply these skills, the goal is to utilize a map of Eau Claire Wisconsin from 1878, and give it a spatial reference, and extract water feature areas from this data, and compare it to the same data just 140 years later in 2018.
Methods
The first portion of this lab is to understand what needs to be done to get to the end goal which is to analyze water feature area. In part one the goal is to georeference the 1878 map of Eau Claire Wisconsin (Figure 1). This process is done through the use of the georeferencing toolbar in ArcMap where the image of the map can be moved and shaped to attempt to align it with the Eau Claire area through using a 2018 centerlines shapefile that shows the middle of all the roads in Eau Claire. (Figure 2). Without the use of GCP points aligning the 1878 image to the current layout is very difficult. However some features over time have not changed as significantly. For instance most roads are still in the same spot or atleast pretty close. At this point of the lab in order to align the 1878 image it was necessary to use GCP points between the 1878 image and the centerlines shapefile. this is done through the georeferencing toolbar in order to warp the image to its correct spatial location. after this the image is georeferenced and aple to be analyzed.
The second half of this lab required creating a feature class, and digitizing polygons for the feature class. The goal is to digitize around all the water features in the 1878 image within a study area, and also the water features within the same study area in 2018. First a file geodatabase was created within my lab 2 folder, here once this was created, a feature class was created and it will contain polygons representing surface water area within the study area. This is done for 1878 image by digitizing over the image area, and for 2018 this is done by digitizing over the topographic basemap within the study area. The 1878 feature class is called Hydro_1878, and the 2018 image is Hydro_2018.
Once these shapefiles are created showing just the surface water area, they both have to be projected to the same projected coordinate system in order to analyze the areas. to do this both were brought into the project tool in ArcMap where they were re projected to the coordinate system NAD_1983_HARN_Adj_WI_EauClaire_Feet. Once they are in the same coordinate system they are then able to be analyzed.
Finally in this lab cartographically pleasing maps were created to show first the georeferenced image of 1878 Eau Claire Wisconsin, then a map showing the change in surface water within a study area in Eau Claire county.
Results
First a map was produced to show the 1878 image georeferenced to align with the basemap and centerlines shapefile (Figure 3). This was done through the use of GCP points and the georeferencing toolbar. A 2nd order polynomial transformation was used with 8 GCP points on this image, and it provided an RMS error of 12.118 which is not great but close enough for this image. An RMS error tells how accurate the correction of the image is. This process of georeferencing is designed to warp the image as close to its source frame as possible. Figure 4 shows the table showing the GCP points, and the Total RMS value.
Next after referencing these images, and digitizing the water features, a map of the water features compared over time was produced (Figure 5). After digitizing both sstudy area water features, the areas of the polygons were focused on. in 1878 the total area of water within the study area was 21,626,499 square feet and 2018 was 20,097,801 square feet. These two areas are pretty close, yet we see that the area actually went down since 1878. This occurs in the movement of rivers over time, surface area can be gained or in this case lost over time.
Sources
Goal and Background
The goal of lab two is to understand how to properly georeference data that does not contain a spacial reference. Additionally, new data will be created to help solve spatial questions.
To apply these skills, the goal is to utilize a map of Eau Claire Wisconsin from 1878, and give it a spatial reference, and extract water feature areas from this data, and compare it to the same data just 140 years later in 2018.
Methods
The first portion of this lab is to understand what needs to be done to get to the end goal which is to analyze water feature area. In part one the goal is to georeference the 1878 map of Eau Claire Wisconsin (Figure 1). This process is done through the use of the georeferencing toolbar in ArcMap where the image of the map can be moved and shaped to attempt to align it with the Eau Claire area through using a 2018 centerlines shapefile that shows the middle of all the roads in Eau Claire. (Figure 2). Without the use of GCP points aligning the 1878 image to the current layout is very difficult. However some features over time have not changed as significantly. For instance most roads are still in the same spot or atleast pretty close. At this point of the lab in order to align the 1878 image it was necessary to use GCP points between the 1878 image and the centerlines shapefile. this is done through the georeferencing toolbar in order to warp the image to its correct spatial location. after this the image is georeferenced and aple to be analyzed.
The second half of this lab required creating a feature class, and digitizing polygons for the feature class. The goal is to digitize around all the water features in the 1878 image within a study area, and also the water features within the same study area in 2018. First a file geodatabase was created within my lab 2 folder, here once this was created, a feature class was created and it will contain polygons representing surface water area within the study area. This is done for 1878 image by digitizing over the image area, and for 2018 this is done by digitizing over the topographic basemap within the study area. The 1878 feature class is called Hydro_1878, and the 2018 image is Hydro_2018.
Once these shapefiles are created showing just the surface water area, they both have to be projected to the same projected coordinate system in order to analyze the areas. to do this both were brought into the project tool in ArcMap where they were re projected to the coordinate system NAD_1983_HARN_Adj_WI_EauClaire_Feet. Once they are in the same coordinate system they are then able to be analyzed.
Finally in this lab cartographically pleasing maps were created to show first the georeferenced image of 1878 Eau Claire Wisconsin, then a map showing the change in surface water within a study area in Eau Claire county.
Figure 1: This is the 1878 Map of of Eau Claire Wisconsin. in this image the map has no reference frame, this is hard to tell however without seeing a background map.
Figure 2: This image shows the 1878 image before it is aligned to the Centerlines shapefile. This image shows how poorly the two align before being Georeferenced through the use of GCP points.
Results
First a map was produced to show the 1878 image georeferenced to align with the basemap and centerlines shapefile (Figure 3). This was done through the use of GCP points and the georeferencing toolbar. A 2nd order polynomial transformation was used with 8 GCP points on this image, and it provided an RMS error of 12.118 which is not great but close enough for this image. An RMS error tells how accurate the correction of the image is. This process of georeferencing is designed to warp the image as close to its source frame as possible. Figure 4 shows the table showing the GCP points, and the Total RMS value.
Next after referencing these images, and digitizing the water features, a map of the water features compared over time was produced (Figure 5). After digitizing both sstudy area water features, the areas of the polygons were focused on. in 1878 the total area of water within the study area was 21,626,499 square feet and 2018 was 20,097,801 square feet. These two areas are pretty close, yet we see that the area actually went down since 1878. This occurs in the movement of rivers over time, surface area can be gained or in this case lost over time.
Figure 3: This map shows the 1878 map of Eau Claire georeferenced and overlayed over a current Eau Claire Basemap. The warp from Georeferencing can be seen on the sides of the image.
Figure 4: This shows the table containing each individual GCP location.
Figure 5: This Map shows how water features have changed in Eau Claire over 140 years (1878-2018).
- David Rumsey Map Collection https://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~4181~480085#
- Master_Centerlines feature class (clipped), Eau Claire County
- World Topographic Map, ESRI, 2018: https://www.arcgis.com/home/item.html?id=30e5fe3149c34df1ba922e6f5bbf808f
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