Exercise 6: Geocoding Fac Sand Mines in Northwestern Wisconsin

Goals and Objectives

The goal of this lab is to become acquainted with the process of geocoding. Geocoding is a geographic technique which finds latitude and longitude coordinates from other geographic data, ZIP codes, street addresses, or PLSS. Students will use ArcMap as the geocoder in order to complete this task. Students will be supplied with a table containing address data for frac sand mines in Northwestern Wisconsin. However, these addresses are incomplete and will require some research in order to locate the mine on an aerial image.

Methods

The first objective in the lab has the student download a file geodatabase for Trempealeau County, Wisconsin. After this data has been explored, we will also download a spreadsheet containing recent locations for frac sand mines in Wisconsin. Upon opening the spreadsheet, it becomes apparent that the formatting of these addresses is not consistent. Some addresses only contain town names, some only contain highway names, and others are left completely blank. It is our goal to research these mines and fill in the table as best as possible in order for geocoding to work successfully.  

The four vital pieces of information we need for geocoding are the facility address, city, zip code, and state. Once this information has been gathered we can begin the geocoding process. One method of geocoding automatically guesses the correct location by using the four vital pieces of information while the other method allows the user to manually place each point instead. Since we have a table that is almost complete with address data, we will let the software guess based on the information we have provided. ArcMap allows us to import our table and apply the geocoding wizard to use certain fields for address location. The geocoding wizard will then return a shapefile with possible candidates for each mine from the original table. If everything works properly, each point should be placed at each property.

 

 

Errors are common during this step, and require that the points be manually placed instead. With the help of an aerial image, manually placing address points can be very accurate once the location and general appearance of the target is known.

 

 

Once all mines were properly located by geocoding, all students submitted their results in the form of a shapefile. Each student’s mines were then merged with eachother to display all the geocoded results from the class. A point distance tool was used to generate a table measuring the distance between each of the mine locations in relation to the rest of the class.

Results

 

 

 

 

 

Discussion

Errors that occurred in this lab are both inherent and operational. Since geographic data is only a representation of the real world, all data is collected, generalized and then symbolized. Taking data from the surface of a spheroid and attempting to translate it onto a 2D surface will never be perfect.  No matter what instruments or procedures are used during data collection, inherent errors will occur naturally. Operational errors occur because of mistakes made by the instruments, processes, or the operator. Slight imperfections in data collection, human bias, table digitizing, and data entry are all considered as operational errors. Errors that resulted in the distances in the point table can mostly be categorized into operational errors. The geocoding tool relied on the user for complete address data in order to find the correct location on the map. The correct placement of each geocoded point relied on the user for confirmation. If the location of a point is not near the target location then it is the fault of the user, not the nature of the geographic data. The best way to investigate which points are correct or incorrect would be to display them over an aerial image and view where some of the locations were placed. Mines are easy to spot using aerial imagery, and google searches can be used to acquire more information regarding the name and address of the mine.

Conclusion

Geocoding is a powerful tool when appropriate data is supplied. With the help of a fully normalized address table, geocoding services within mapping software can pinpoint the locations of the target entities. Operational errors are inevitable, proven by the varied data points supplied by the class.