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otl-year-built

Leaflet map of parcels by year/decade/century built to display history of property development in West Hartford CT, for https://OnTheLine.trincoll.edu

Live map

https://ontheline.github.io/otl-year-built/index-caption.html

Credits

Interactive map developed by Jack Dougherty and Ilya Ilyankou / Picturedigits for On The Line, http://OnTheLine.trincoll.edu, Trinity College, Hartford CT

Source Data and Notes

Shapefiles with parcel identifiers and year-built data provided by Town of West Hartford and AppGeo in June 2021 from the Online Assessment Database https://gis.vgsi.com/westhartfordct/. Thanks to Jared Morin ([email protected]) and Rebecca Talamini ([email protected]).

Note that "yearbuilt" means "most recent year of construction recorded for this parcel" because this present-day assessment database was not designed to be a complete historical record of all property development. For example, it does not record when a building was first erected on a property (e.g. 1910), then torn down (e.g. 1970), because only the most recent date of construction is stored (e.g. 1970). Also, "yearbuilt" data missing for about 600 out of nearly 20,000 parcels (3%), which are included in a separate file no-year-built.geojson but not displayed in the interactive map. Only properties that currently exist are shown in this present-day assessment database.

Based on "yearbuilt", we added a new field named "decadebuilt" where "1900s" means 1900-1909, "1910s" means 1910-1919, etc. "Pre1900" means all years before 1900.

GIS_Area is measured in acres (eg. 4 Frederick Road = 0.16 acres)

screenshot

Data Cleaning and GeoJSON Conversion

Shapefiles processed by Jack Dougherty in https://Mapshaper.org to clean duplicates (condos and other units on same parcel with same or similar street address), create decadebuilt column, and to convert to GeoJSON files.

  • Uploaded shapefiles.zip to Mapshaper.org
  • ignore 23 line intersections
  • console: -proj wgs84
  • console: -split ParcelType, which divided into different files by type:
    • 20,042 Parcel
    • 2,387 Condo Main
    • 22 unnamed
    • 1 Water (ignore)
    • 1 Private ROW (ignore)
    • 1 Paper Street (ignore)
  • Export into separate geojson files
  • Also, export Condo Main into CSV and create pivot table by ParcelID and yearbuilt. Note that 56 features have multiple entries (units on same lot) but same ParcelID and same GIS_Area (where each condo is listed as the entire property lot, so needed to eliminate duplicates)
  • Upload only the Condo predissolved geojson file, where multiple condos have same ParcelID (but slightly different addresses), and use console to dissolve but "copy" (aka keep) first instance of selected fields into the dissolved feature.
    • console: $ dissolve ParcelID copy-fields=ParcelID,ParcelType,siteaddres,GIS_Area,yearbuilt
    • [dissolve] Dissolved 2,387 features into 56 features
  • Manually assign decadebuilt field to Condo CSV, and join to Condo GeoJSON
  • Upload only Parcels predissolved geojson, where a few hundred multiple units have same ParcelID (similar to condos), and dissolve but keep first instance as above.
    • $ dissolve ParcelID copy-fields=ParcelID,ParcelType,siteaddres,GIS_Area,yearbuilt
    • [dissolve] Dissolved 20,042 features into 19,865 features
  • Upload only unnamed GeoJSON, export CSV, and join in decadebuilt field. About 20 rows are empty and must be ignored.
  • -merge-layers target=WH-Parcel-decadebuilt,WH-Condo-decadebuilt,WH-unnamed-decadebuilt
  • simplified 100MB fullsize GeoJSON down 50% (large, 50MB) in order to upload to GitHub, and simplified at 0.5% (simplified, 11MB) 11MB, which you think would be even smaller, but it's not
  • -split decadebuilt (to produce one GeoJSON file for each decade/century)
  • downloaded WH-yearbuilt.csv and created pivot table to show results

Results

Decade-Century Built Count Percent
1700 25 0%
1800 25 0%
1850 162 1%
1900 205 1%
1910 784 4%
1920 3019 15%
1930 2183 11%
1940 3020 15%
1950 6199 31%
1960 2181 11%
1970 742 4%
1980 306 2%
1990 179 1%
2000 206 1%
2010 90 0%
2020 7 0%
na 594 3%
Total 19927 100%
Decade-Century Built Acres Percent
1700 24 0%
1800 117 1%
1850 78 1%
1900 111 1%
1910 248 2%
1920 797 6%
1930 810 6%
1940 940 8%
1950 2949 24%
1960 3123 25%
1970 560 4%
1980 309 2%
1990 172 1%
2000 407 3%
2010 145 1%
2020 3 0%
na 1721 14%
Total 12517 100%

Acres based on sum of GIS_Area