Geocoding with census data and the Census API

For my online GIS class I have a tutorial on creating an address locator using street centerline data in ArcGIS. Eventually I would like to put all of my class online, but for now I am just sharing that one, as I’ve forwarded it alot recently.

That tutorial used local street centerline data in Dallas that you can download from Dallas’s open data site. It also gives directions on how to use an online ESRI geocoding service — which Dallas has. But what if those are not an option? A student recently wanted to geocode data from San Antonio, and the only street data file they publicly provide lacks the beginning and ending street number.

That data is insufficient to create an address locator. It is also the case that the road data you can download from the census’s web interface lacks this data. But you can download street centerline data with beginning and end addresses from the census from the FTP site. For example here is the url that contains the streets with the address features. To use that you just have to figure out what state and county you are interested in downloaded. The census even has ESRI address locators already made for you using 2012 data at the state level. Again you just need to figure out your states number and download it.

Once you download the data with the begin and ending street numbers you can follow along with that tutorial the same as the public data.

Previously I’ve written about using the Google geocoding API. If you just have crime data from one jurisdiction, it is simple to make a geocoder for just that locality. But if you have data for many cities (say if you were geocoding home addresses) this can be more difficult. An alternative online API to google that does not have daily limits is the Census Geocoding API.

Here is a simple example in R of calling the census API and geocoding a list of addresses.

library(httr)
library(jsonlite)

get_CensusAdd <- function(street,city,state,zip,benchmark=4){
    base <- "https://geocoding.geo.census.gov/geocoder/locations/address?"
    soup <- GET(url=base,query=list(street=street,city=city,state=state,zip=zip,format='json',benchmark=benchmark))
    dat <- fromJSON(content(soup,as='text'), simplifyVector=TRUE)
    D_dat <- dat$result$addressMatches
    if (length(D_dat) > 1){
    return(c(D_dat['matchedAddress'],D_dat['coordinates'][[1]])) #error will just return null, x[1] is lon, x[2] is lat
    }
    else {return(c('',NA,NA))}
}

#now create function to loop over data frame and return set of addresses
geo_CensusTIGER <- function(street,city,state,zip,sleep=1,benchmark=4){
  #make empy matrix
  l <- length(street)
  MyDat <- data.frame(matrix(nrow=l,ncol=3))
  names(MyDat) <- c("MatchedAdd","Lon","Lat")
  for (i in 1:l){
    x <- suppressMessages(get_CensusAdd(street=street[i],city=city[i],state=state[i],zip=zip[i],benchmark=benchmark))
    if (length(x) > 0){
        MyDat[i,1] <- x[1]
        MyDat[i,2] <- x[2]
        MyDat[i,3] <- x[3]
    }
    Sys.sleep(sleep)
  }
  MyDat$street <- street
  MyDat$city <- city
  MyDat$zip <- zip
  MyDat$state <- state
  return(MyDat)
}

## Arbitrary dataframe for an exercise
AddList <- data.frame(
  IdNum = c(1,2,3,4,5),
  Address = c("450 W Harwood Rd", "2878 Fake St", "2775 N Collin St", "2775 N Collins St", "Lakewood Blvd and W Shore Dr"),
  City = c("Hurst", "Richardson", "Arlington", "Arlington", "Dallas"),
  State = c("TX", "TX", "TX", "TX", "TX")
)

test <- geo_CensusTIGER(street=AddList$Address,city=AddList$City,state=AddList$State,zip=rep('',5))

If you check out the results, you will see that this API does not appear to do fuzzy matching. 2775 N Collin St failed, whereas 2775 N Collins St was able to return a match. You can also see though it will return an intersection, but in my tests "/" did not work (so in R you can simply use gsub to replace different intersection types with and). I haven’t experimented with it too much, so let me know if you have any other insight into this API.

I will follow up in another post a python function to use the Census geocoding API, as well as using the Nominatim online geocoding API, which you can use for addresses outside of the United States.

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