Methods & Analysis
Map 1 - Properties/Current and Future Floodplain
- Retrieved property data from Hope (not geo-located and with not practical BBL numbers) and from Ascendant (already geo-located but with projection issues)
- Re-coded BBL numbers for both properties from scratch through padding numbers and concatenation
- Conversion Tool - Convert Exl into Table
- Table join between properties BBL and Mapluto BBLs for Manhattan but 6/100 properties did not join. I figured out that some addresses that I had initially split into two (e.g. 242-244 East 106 Street) should be kept as one because splitting them generates a new BBL code that of course does not exist. After I joined the address back I solved 5 of 6 missing BBL which were not joining.
- Selected all null (not joint attributes) and selected inverse to obtain only BBLs in CD 10 and 11, where properties are located. Exported data selection as shapefile.
- Created 1 field per floodplain (2015, 2020, 2050) set with a short integer and all values at 0 (NOT IN FLOODLAIN). From the FEMA 2015 I selected by attribute only the 100 year floodplain
- Selected by location - from the BBL with condition of intersecting with floodplain 2015, 2020, 2050, 2080. Each time I selected with field calculator BBLs that intersected with each floodplain and I assigned the intersection at 1 (IN FLOODPLAIN)
- Created another column where I aggregated all numbers to understand the BBLs that fall in the floodplain at none, one, two or all projections.
- I decided to represent the different floodplains in three colors and code the properties (1 Ascendant; 0 Hope) and assign different colors to both. Another way I could have done this was to color code the chronology of flooding from green to red depending on 3 (floods in 2020), 2 (floods in 2050), 3 (floods in 2080) but I realized I also needed to distinguish the properties. I tried do choose "Many values" under Symbology and assign both coding for floodplain and coding for type of property (distinguishing them through a specific pattern applied to a solid color). The result was not satisfying because, especially in the overall map the zoom levels are not appropriate to show the details of the patterning.
- Exported Attribute table to Excel and performed a yearly rate of change analysis on the total number of buildings exposed to different floodplains as well as yearly rate of change for each property type. I used the following formula:
=(new_value-original_value)/(original_value)
where original_value represents the value that the percentage of change is based on, and new_value represents the value that has changed.
I then divided what I obtained by the number of years (2080-2015) that is 65
Maps 2, 3, 4, 5 - Small Multiple maps of single floodplains
- Created 4 small multiple maps showing a zoomed in version of Map 1. The zooms were chosen based on where it most flooded in each projection.
Map 6 - Comparison with yearly rate of flooding of all buildings in Central and East Manhattan
Compare the rate of change All properties in the CDs run the same analysis
Map 7 - Average H&A properties elevation in relation to floodplain hazard
For this maps I wanted to show how elevation may affect H&A BBLs being flooded under different floodplains. I used Zonal Statistics via Table, where under "Input raster or feature zone data" I selected the H&A BBLs properties, in Zone field I selected 'BBL' under "Input value raster" the DEM clipped and mask to Central and East Harlem. Under statistics type I choose MEAN and I repeated the operation to obtain the MEDIAN elevation of the properties. I made a Table join on "BBL" between the table produced by zonal statistics and the table with H&A properties. I then opened the table and on MEAN I chose ' Summarize SUM Floodplain' to the average MEAN elevation and saved it outside the geodatabase as text file so I could work it on Excel. The result is a table that expresses the average elevation at which BBLs flooded under different flood scenarios.