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.
