Adam Knight

Lesson 2

Manipulating and Summarizing Attribute Data

Penn State University

Figure 1: April 27th, 2011 Tornado Paths and Intensity based on Fujita Scale between F1 and F5.  F5 tornados are the most powerful and are shown in dark red lines. Most of the tornado activity was in Central and Northern Alabama.  Map Display Units are in Miles.

On April 27th, 2011, the state of Alabama experienced one of the most violent outbreaks of tornado activity ever recorded in the United States.  There were as many as 62 tornados across the state and 29 confirmed tornados in central Alabama that day.  The size and power of the tornados were of note. For this lesson we will be examining the total destruction from different views on the map on the Alabama County level.  The criteria we will be to looking at will be: Property Damaged, Property Destroyed, Property Destroyed in Dollars, Housing Unit Densities per County, and Housing Densities per Census Tracts. Our final goal will be to define the total damage by joining tables, adding, and population fields for desired thematic maps illustrating this relationship.  The coordinate system used for this map is based off the NAD_1983_UTM_Zone_16N.

Figure 2: Total Damage for Housing Units that were not completely destroyed.

The maps were created by joining attributes in the countydamage.bdf table to the Counties_Project layer utilizing the FIPS shared attribute. FIPS (Federal Information Processing Standard) are codes assigned as identifiers for each state and county. Once we have validated the join, we need to populate the county demographic information from each county.  This basic Census data can be found within the countystatistics.dbf table.  The tornado paths themselves are found within the TornadoAttribs.dbf tables.  The combined tables now reside within the “tornadocounties” layer.  It is from this we can now perform a thematic adjustment to known data.  By selecting the layer properties, we can click on the “Symbology tab” to perform a color ramp of 6 classes of data using the Quantile classification.  The map legend to the left is showing the counties of Tuscaloosa and Jefferson have most damage as shown by the darker green colors.  The total_damage field is calculated by adding the known values of Housing, Apartment, Mobile Home units damaged.

Figure 3: Total Destruction by County.  Total Destruction is total property lost or unrepairable housing.

The map above is showing a thematic color display of total damage property that is unrepairable.  The concentration of the most total destruction resides with counties of Tuscaloosa and Jefferson.  The field of tot_destr was calculated by adding known Housing, Apartments, and Mobile Homes completely destroyed.  The legend on the left side of Figure 3 is showing approximately 2375 units/housing/apartment/mobile homes were destroyed within Tuscaloosa County (dark red), followed by Jefferson County.  

Figure 4: Property Destroyed in Dollars.  Tuscaloosa County sustained over $253,175,000.00 in total losses shown in dark green.

The next map is showing the dollar amounts lost associated with the property destruction.  This map was created by multiplying the tot_destr field by the MEDIAN_VAL field.  The result gives a total amount of $253,175,000.00 was caused in Tuscaloosa County that day.  The Tuscaloosa field was given by multiplying the Median Value of $106600.00 times the total destruction of 2375 housing units lost which gives a total of $253,175,000.00.   Or this could be stated as tot_dollar = tot_destr * MEDIAN_VAL.

Figure 6: Housing Density per County.  Jefferson County has the most dense housing units in Alabama as shown in Dark Purple.

The next thematic map created shows housing densities per county.  This is useful when selecting the other layers of the map showing a correlation between the numbers of houses per square vs. damage.  This was calculated by taking the table data Housing Units divided by Area per square mile. The legend of the left of Figure 6 is showing the highest density with Jefferson County.  This could be represented by the calculation of the total number of housing units (248079) divided by Area per square mile (1122.92) which gives an average of 220.92 units per square mile as shown in Dark Purple.

Figure 7:  Housing Density in Alabama per Census Tracts.  Jefferson County has been zoomed in on to show the densest areas in red.  Tuscaloosa County is shown on the lower left.

For the final thematic map, we have mapped housing densities on the Census Tract level to give a more detailed display.  The map above was created by joining the demographic table data to the Census tracts layer.  The data has been classified using the Quantile method to better highlight population groupings.  The legend of the left is showing the highest concentration of people within Jefferson County with an average of 9655.17 people per square mile.  From this display, we can track the red tornado lines thru the most densely populated areas of the state.

In summary, thematic maps can be used in a multitude of ways to correlate spatial relationships between property damaged, property destroyed, property destroyed in Dollars, housing unit densities per county, and housing densities per census tracts during the massive tornado outbreak on April 27th, 2011 in Alabama.  By selecting the different layers on the map, we can see these relationships represented in color ramped displayed to show the hardest hit areas.

References:

King, E., Walrath, D & Zeiders, M (1999-2014). Problem-Solving with GIS, Lesson 1. The Pennsylvania State University World Campus Certificate/MGIS Programs in GIS.     Retrieved October 12th, 2014.