DOI: 10.3886/icpsr38580.v2
title: National Neighborhood Data Archive (NaNDA): Street Connectivity by Census Tract and ZIP Code Tabulation Area, United States, 2010 and 2020
title: Version 2

description: This study contains measures of street connectivity (how well streets connect with one another) within all United States census tracts and United States ZIP code tabulation areas (ZCTAs). This includes measures of the number of street segments (links) and intersections (nodes) per tract/ZCTA, street length within tracts/ZCTA, and indices representing overall connectivity within the tract/ZCTA.
description: These data characterize street connectivity across all United States census tracts and ZIP code tabulation areas. Street connectivity is a measure of how many paths are available from one destination to the next (e.g. home and shopping), and how direct those paths are.
description: The research team measured street connectivity following the method outlined in Berrigan et al. (2010), which employs the following concepts to represent street connectivity:
Links: street lengths. These are segments of streets between intersections; for example, one rectangular city block would be bounded by four links.
Nodes: endpoints of links, which may be intersections or dead ends. Nodes at three-way or four-way intersections (i.e. those where a traveler makes a route choice) are referred to as real nodes.
Buffers: areas over which to calculate street connectivity. Where Berrigan et al. used a 0.785 km2 buffer to calculate their connectivity measures, the current study used the area of the census tract or ZIP code tabulation area (ZCTA) in square miles.
Circuits: a connected path along streets, starting and ending at the same node.
Berrigan's nine measures of street connectivity were calculated for each tract/ZCTA:
Link/node ratio: total links divided by total nodes.
Intersection density: total real nodes divided by tract/ZCTA area.
Street network density: sum of length of all links within the census tract/ZCTA divided by tract/ZCTA area.
Connected node ratio: real nodes divided by total nodes.
Block density: total census blocks (which usually match street blocks) in the tract/ZCTA divided by tract/ZCTA area.
Average block length: average length of streets within the tract/ZCTA. (Unlike Berrigan, this does not include street length outside the buffer [tract/ZCTA] because street segments, unlike buffers around a point, do not extend beyond census block boundaries.
Median block length: median length of streets within the tract/ZCTA. (Like average block length, this does not include street length outside the buffer.)
Gamma index: ratio of total links fully in the tract/ZCTA to the maximum possible number of links in the tract/ZCTA (3 * (# nodes -2)). (Gamma cannot be calculated and is therefore missing for areas with less than 3 nodes.)
Alpha index: ratio of actual circuits (# links - # nodes + 1) to maximum circuits (2 * (# nodes) - 5). (Alpha cannot be calculated and is therefore missing for areas with less than 3 nodes and in areas where the number of nodes equals or exceeds the number of links.)
Areas with high levels of street connectivity are characterized by high link/node ratios, intersection density, street network density, connected node ratios, and block density; by low average and median block length; and by high gamma and alpha values.
description: Datasets: 
DS0: Study-Level Files
DS1: Street Connectivity by Census Tract 2010 Data
DS2: Street Connectivity by ZIP Code Tabulation Area 2010 Data
DS3: Street Connectivity by Census Tract 2020 Data
DS4: Street Connectivity by ZIP Code Tabulation Area 2020 Data
description: Streets in all census tracts and ZIP code tabulation areas within the United States, excluding the US island territories. Smallest Geographic Unit: census tract and ZIP code tabulation area (ZCTA)
description: Data and documentation for the census tract-level data were originally deposited in openICPSR project 110641.
Data and documentation for the ZCTA-level data were originally deposited in openICPSR project 134561.A ZIP code to ZCTA crosswalk must be used to combine this dataset with ZIP code geocoded data. A crosswalk and sample code for merging the crosswalk with National Neighborhood Data Archive (NaNDA) datasets are available in the ICPSR Linkage Library.For additional information, see the National Neighborhood Data Archive (NaNDA).