NC Census Map
From charlesreid1
MY goal in making this map of North Carolina was to gain more familiarity with the Census Reporter API, and start to dig down past the county level, to the zip code, area code, and census tract levels.
Contents
Starting Point
State and County Data
I started out with some code I wrote for my Census Map, which grabbed California county information, except this time I wrote a code that would turn state names and abbreviations into FIPS codes (here: http://www.census.gov/geo/reference/ansi_statetables.html), necessary to obtain geographic information from the Census Bureau or from Census Reporter, whose lovely API I was using.
STATE|STUSAB|STATE_NAME|STATENS 01|AL|Alabama|01779775 02|AK|Alaska|01785533 04|AZ|Arizona|01779777 05|AR|Arkansas|00068085 06|CA|California|01779778 08|CO|Colorado|01779779 09|CT|Connecticut|01779780 10|DE|Delaware|01779781 11|DC|District of Columbia|01702382 12|FL|Florida|00294478 13|GA|Georgia|01705317 15|HI|Hawaii|01779782 16|ID|Idaho|01779783 17|IL|Illinois|01779784 18|IN|Indiana|00448508 19|IA|Iowa|01779785 20|KS|Kansas|00481813 21|KY|Kentucky|01779786 22|LA|Louisiana|01629543 23|ME|Maine|01779787 24|MD|Maryland|01714934 25|MA|Massachusetts|00606926 26|MI|Michigan|01779789 27|MN|Minnesota|00662849 28|MS|Mississippi|01779790 29|MO|Missouri|01779791 30|MT|Montana|00767982 31|NE|Nebraska|01779792 32|NV|Nevada|01779793 33|NH|New Hampshire|01779794 34|NJ|New Jersey|01779795 35|NM|New Mexico|00897535 36|NY|New York|01779796 37|NC|North Carolina|01027616 38|ND|North Dakota|01779797 39|OH|Ohio|01085497 40|OK|Oklahoma|01102857 41|OR|Oregon|01155107 42|PA|Pennsylvania|01779798 44|RI|Rhode Island|01219835 45|SC|South Carolina|01779799 46|SD|South Dakota|01785534 47|TN|Tennessee|01325873 48|TX|Texas|01779801 49|UT|Utah|01455989 50|VT|Vermont|01779802 51|VA|Virginia|01779803 53|WA|Washington|01779804 54|WV|West Virginia|01779805 55|WI|Wisconsin|01779806 56|WY|Wyoming|01779807 60|AS|American Samoa|01802701 66|GU|Guam|01802705 69|MP|Northern Mariana Islands|01779809 72|PR|Puerto Rico|01779808 74|UM|U.S. Minor Outlying Islands|01878752 78|VI|U.S. Virgin Islands|01802710
Further Sub-Levels
Via the Census Bureau's own technical documentation, http://www.census.gov/prod/cen2010/doc/sf1.pdf (it is very extensive), we can obtain the following geographical entity hierarchy:
Next, I headed over to the Census Reporter API documentation: https://github.com/censusreporter/census-api/blob/master/API.md
This didn't say anything specific about geographies below the county level, so I assumed they were there, I just needed to request them correctly.
Sure enough, I grabbed the geoid for Dare County, NC, which was 05000US37055.
I then fed that geoid to the Census Reporter API, and it gave me information about the county:
$ curl "http://api.censusreporter.org/1.0/geo/tiger2013/05000US37055"
{"geometry": null, "type": "Feature", "properties": {"awater": 3054395108, "display_name": "Dare County, NC", "simple_name": "Dare County", "sumlevel": "050", "population": 34289, "full_geoid": "05000US37055", "aland": 992627006}}
and geometry information:
$ curl "http://api.censusreporter.org/1.0/geo/tiger2013/05000US37055?geom=True"
{"geometry": {"type": "MultiPolygon", "coordinates": [[[[-75.76384399999999, 35.233886], [-75.868684, 35.579451999999996], [-75.879179, 35.604172], [-75.87683299999999, 35.628116999999996], [-75.88395299999999, 35.632784], [-75.891953, 35.643328], [-75.890496, 35.652259], [-75.89834499999999, 35.661057], [-75.901164, 35.668997999999995], [-76.027445, 35.669094], [-76.03084299999999, 35.663227], [-76.035266, 35.662022], [-76.045987, 35.666117], [-76.029265, 35.682038999999996], [-76.022328, 35.709224999999996], [-76.025088, 35.721156], [-76.01927599999999, 35.752763], [-76.02239, 35.81066], [-76.01769399999999, 35.865356], [-76.00917799999999, 35.894453], [-75.987466, 35.916453], [-75.978991, 35.964459999999995], [-75.963734, 35.984291999999996], [-75.948736, 35.994425], [-75.78040899999999, 36.047422999999995], [-75.767448, 36.055639], [-75.763783, 36.062792], [-75.763192, 36.074594], [-75.77425, 36.103245], [-75.776439, 36.135726999999996], [-75.77865899999999, 36.142323999999995], [-75.789363, 36.154436], [-75.789075, 36.172205999999996], [-75.80169599999999, 36.187985], [-75.79943, 36.202217999999995], [-75.813189, 36.223544], [-75.70907799999999, 36.244983999999995], [-75.666246, 36.148924], [-75.566047, 35.975614], [-75.48050099999999, 35.814206999999996], [-75.46623699999999, 35.801314999999995], [-75.460815, 35.784524], [-75.437617, 35.74696], [-75.41781999999999, 35.686082], [-75.406815, 35.636972], [-75.40039, 35.593512], [-75.400849, 35.558718], [-75.402422, 35.54421], [-75.415089, 35.50018], [-75.426135, 35.386922999999996], [-75.447751, 35.309794], [-75.459334, 35.246552], [-75.468477, 35.21519], [-75.484571, 35.187577], [-75.505059, 35.174426], [-75.53217599999999, 35.167148999999995], [-75.55758399999999, 35.170535], [-75.581108, 35.183783999999996], [-75.59536899999999, 35.182826999999996], [-75.63621499999999, 35.172205], [-75.70737, 35.146111], [-75.73662, 35.140564999999995], [-75.76384399999999, 35.233886]]]]}, "type": "Feature", "properties": {"awater": 3054395108, "display_name": "Dare County, NC", "simple_name": "Dare County", "sumlevel": "050", "population": 34289, "full_geoid": "05000US37055", "aland": 992627006}}
Well, nothing contained in that JSON about sub-levels...
There is code for adding a tile layer to, e.g., a Leaflet map, using this URL:
http://api.censusreporter.org/1.0/geo/tiger2013/tiles/<sumlevel>/<zoom>/<x>/<y>.geojson
But this wouldn't accomplish the goal of getting GeoJSON data falling within a given county - it would get GeoJSON data for a map tile.
The solution is to request information about a particular level of geogrpahic entites, and pass it a geo_id to restrict the search. This can be done using the following API URL:
http://api.censusreporter.org/1.0/geo/show/tiger2013?geo_ids=<geo entity level>|<geo id>
So to find information about census tracts, which were level 140 (different levels and corresponding codes are listed on this page: [1]), for Dare County, North Carolina, which has geoid 05000US37055, we would request the URL:
http://api.censusreporter.org/1.0/geo/show/tiger2013?geo_ids=140|05000US37055
Downloading Census Tract Data for Counties
As mentioned, I used the following API URL to get census tract boundaries for Dare County, North Carolina:
$ curl http://api.censusreporter.org/1.0/geo/show/tiger2013?geo_ids=140|05000US37055
Using curl, from the command line, returns the JSON to stdout. We can capture it in a JSON file by saying:
$ curl http://api.censusreporter.org/1.0/geo/show/tiger2013?geo_ids=140|05000US37055 > dare_county_nc.json
Now we can drop that JSON file as a layer onto our Leaflet map, and voila! we have our census tracts:
Map Plan
My plan for the map is to use Python to loop over a list of particular counties, request all census tracts for those counties, and map them.
Overlay of Census Tracts
There are two ways to overlay census tracts.
Download GeoJson
The first way is to download the GeoJson to a file, and serve it yourself. In this case, your Javascript will look like this:
var geoj = new L.geoJson.ajax("dare_census_tracts.json",{onEachFeature:enhanceLayer}).addTo(map);
Grab GeoJson from URL
The other, more seamless option is to get the Json directly from the API of Census Reporter. You can do this with the following code (requires jQuery):
rooturl = "http://api.censusreporter.org/1.0/geo/show/tiger2013?geo_ids=140|05000US37055";
$.ajax({
type: "GET",
url: rooturl,
success: function (data) {
var geojson = new L.geoJson(data, {
style: {
fillColor: '#CFC',
fillOpacity: 0.20,
stroke: true,
color: '#222',
weight: 1
},
onEachFeature: function(feature, layer){
popupText = "";
popupText += feature.properties.name;
}
}).addTo(map2);
}
});