ENVIRONMENTAL STUDIES Copyright 2020 Two centuries of

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SCIENCE ADVANCES RESEARCH ARTICLE, In addition to new land based assessments of urban change and between settlement measures and population growth We estimate. development these novel data also unlock new opportunities to that on average each additional built up property at the county. model the spatial distribution of population in the past Our moti level is associated with around 2 to 2 25 additional people with. vation in this regard is rooted in recent research First while recent some regional variation This finding is notable as there are at pres. work shows relationships between historical population counts and ent no reliable estimates of long term fine resolution population. built up property attributes this analysis is confined to the national growth for the United States Thus we argue and demonstrate that. scale and lacks the spatial detail necessary for understanding varia the novel HISDAC US data provide an unprecedented opportunity. tion and change 21 Second data on developed or built up land to study and understand long term urbanization and settlement. are often used as the main ancillary variable in population modeling processes at fine spatial and temporal granularity from the begin. using dasymetric refinement approaches This refinement method ning of the 19th century to today. is a form of areal interpolation that makes use of relationships be. tween the target variable population and the ancillary variables used. for subunit estimation e g 22 25 Third parcel data combined RESULTS. with population and road network data were used in recent efforts Taking a land perspective on urbanization Where when. to study long term urbanization processes within U S cities 26 and how much land was built up. but such data have not been available for the entire nation to date Using the fine temporal and spatial granularity as well as different. Last researchers applied similar principles of land availability and built characteristics we elucidate new spatiotemporal settlement. suitability to disaggregated historical census summary statistics and patterns With these patterns we draw a detailed picture of the evo. created fine resolution population distributions 27 However these lution of built up land use in the conterminous United States from. Downloaded from http advances sciencemag org on July 27 2020. approaches lack robust testing and validation for the years before 1810 to 2015. 2000 Given this body of research we argue that data products such Mapping the earliest recorded built up properties FBUY within. as the HISDAC US provide unique opportunities to model not only boundaries of varying spatial scale we find that urban development. changes in the built environment but also potentially fine grained trends are strongly dependent on the size of the spatial unit used broad. historical population estimates Progress in this area could unlock new national to local Fig 1 By using the contemporary county bound. possibilities for the spatiotemporal analysis of urbanization in the United aries of the 2010 decennial census as consistent mapping units we. States combining both land and population based perspectives observe two primary well known national trends Fig 1 A and B. While our main findings confirm well known broad diffusion First we find trends of urban development diffusing westward from. patterns of urbanization HISDAC US settlement layers enable us Northeastern and coastal Southern states into the interior of the. to identify detailed building trajectories as well as expansion and United States including the eastern parts of Texas Kansas and. densification patterns at various spatial scales The fine granularity Arkansas These trends unfold later in the Appalachian Mountains. of the data is depicted by maps of the FBUY Fig 1 and the number and parts of Florida likely because of the rough topography and lim. of built up property records BUILD Fig 2 B to F from 1810 to ited habitability of these areas Second while buildings in counties in. 2010 Finer scale data break down broader national and regional the central and western states of the United States tend to be newer. development trends and describe for example local processes of than their Eastern counterparts there are isolated counties across the. expanding urban and suburban areas or infilling in built up places western seaboard and interior regions e g Denver and Wichita. during different time periods We also demonstrate relationships Falls Fig 1 D and E that experienced particularly early waves of. Fig 1 Maps of the FBUY at different levels of granularity The maps depict national regional and local scale processes of human development A county level. FBUY within contemporary Census 2010 boundaries used as constant units of analysis over time counties where no built up year is available are shown in gray more. detailed distributions of FBUY for the states of Colorado Kansas and Ohio within B county boundaries C 2500 m grid cells and D 250 m grid cells respectively E A. detailed depiction of the 250 m resolution data for the cities of Denver CO Wichita Falls KS and Columbus OH. Leyk et al Sci Adv 2020 6 eaba2937 3 June 2020 2 of 12. SCIENCE ADVANCES RESEARCH ARTICLE, Downloaded from http advances sciencemag org on July 27 2020. Fig 2 HISDAC US settlement layers derived from the ZTRAX data at fine granularity for different points in time The layers are shown at 250 m spatial resolution. for different points in time 1810 2010 for Rockingham County NH and surroundings including A FBUY layer in which raster cells are assigned the earliest built year. recorded and a time series of the number of built up property records BUILD located within a raster cell in B 1810 C 1860 D 1910 E 1960 and F 2010 County. boundaries of the 2010 census are shown in black, development relative to the rest of their respective states In many different resolutions to more holistically measure local and regional. instances these nodes of early development predate the demarcation development trends As discussed above these settlement measures. of these regions as U S states include the total number of built up properties BUILD the BUI of. By assigning FBUY values to smaller spatial units such as indi land derived from the sum of indoor floor area of existing built up. vidual grid cells of specific size e g 2 500 m resolution Fig 1C or properties and the number of grid cells built up within a chosen unit. 250 m resolution Figs 1D and 2A we are able to assess local settle or BUA see Materials and Methods for details We extracted these. ment trends within consistent spatial units that break down the variables within consistent spatial units across time periods to gener. county level patterns For example early settlement and growth ate long term trajectories e g fig S2 at the state level and multitem. along Colorado s Front Range emanates from a number of isolated poral spatial distributions e g fig S3 at the county level to characterize. centers with Denver being the largest Fig 1 D and E left Also variation in settlement patterns over time We illustrate county level. earliest records of development in more rural settings of the state estimates of BUILD and its change every 5 years between 1810 and. in mountainous areas or in the plains appear spatially related to 2015 and spatial clusters for each point in time movie S1 However. streams and topographic conditions that facilitated development the full details of local settlement processes can only be uncovered at. livelihood access to water and transportation In contrast new de the finest granularity. velopment in Kansas spreads as a broader national pattern of west Taking Rockingham County NH and the areas surrounding. ward expansion rather than as sprawl from discrete larger urban New Hampshire and Massachusetts as an example region we trace. hubs Fig 1 D and E middle In Ohio urban centers begin to spatial distributions of BUILD at the finest spatial resolution of. overlap over time as they expand into one another Fig 1 D and E 250 m over five points in time 1810 1860 1910 1960 and 2010. right These patterns illustrate the opportunities provided by such Fig 2 B to F This analysis allows us to track the number of built. multiresolution data for detecting local to regional scale settlement up property records at the grid cell level and better understand local. and land development trends over long time periods urban growth processes In this particular case the cities of Manchester. We used the built year of each property in combination with build NH Newburyport MA Amesbury MA and Portsmouth NH grew. ing attributes to compute time series of various settlement variables at as separate small urban hubs until 1860 Fewer built up properties. Leyk et al Sci Adv 2020 6 eaba2937 3 June 2020 3 of 12. SCIENCE ADVANCES RESEARCH ARTICLE, were established in rural parts of the area along roads during the. early and mid 1800s By 1910 Manchester grew substantially in area. and density while the port cities developed at slower rates This. trend continued and by 1960 low density settlement in rural areas. had expanded along roads to increasingly connect higher density. urban hubs Furthermore during this time period development. increased rapidly along the coastline Last by 2010 the area had expe. rienced intensified sprawl in its southern and coastal regions a con. tinued expansion of urban hubs and increasing densification in the. South which grew into a larger urban and suburban conglomerate. Such subcounty temporal settlement patterns have the potential to. yield vast new insight into the geographical unfolding and intensity. of local urban development processes, Land based measures of change characterize types of urban.
development at varying scales, Fine scale settlement layers provide unique opportunities to distinguish. between land based processes of urbanization such as expansion and den. sification Expansion refers to the amount or proportion of new devel. Downloaded from http advances sciencemag org on July 27 2020. oped area over time and densification is the ratio of the change in BUI. to the change in BUA over time see details in Materials and Methods. Coarser scale county level maps of expansion and densification. reveal notable regional variation see fig S4 and movie S1 for a. complete sequence of those maps and their spatial cluster maps. These results complement the observed regional settlement pat. terns but provide more details about the underlying processes of. urban growth often a function of time infrastructure and access to. technology Maps of peak timing of densification and expansion. fig S5 reveal that both processes are temporally associated and. vary regionally For example along the coastlines of the Southeast. and the Southwest of the United States the vast majority of counties. have expansion peaks earlier than densification indicative of land. expansion maxima followed by maximum infilling in already built up. areas We found the opposite process in the noncoastal Northeast. the Midwest and parts of the Mountain West In these areas devel. opment and peak densification occurred over the early to mid. 1900s and expansion often in the form of sprawl subsequently. unfolded and peaked during the second half of the 20th century. We assessed city level measures of expansion and densification. for San Francisco CA Atlanta GA and Boston MA Fig 3A With. the exception of the time period from 1920 to 1950 which was a period. Fig 3 Settlement trends and multitemporal distributions for San Francisco. of rapid rise and decline in terms of expansion and densification in. Atlanta and Boston A Time series of densification and expansion calculated. Boston both measures trended gradually upward over time but took over 15 year time increments computed within metropolitan statistical area bound. opposite trends after 2000 expansion declining and densification rising aries of 2010 B New built up grid cells indicated by black grid cells during the. Atlanta and San Francisco exhibit more notable variation In the given time periods C Change in BUI i e the sum of building indoor area per grid. sprawling city of Atlanta densification has remained modest with cell during the given time periods with warmer colors indicating greater change. some recent increases but expansion has markedly increased since. the mid 20th century Over the past decade Atlanta had decreasing B and C respectively we gain insight into the development mech. expansion and increasing densification For San Francisco in contrast anisms generating differences across cities The spatial patterns sug. we find the opposite pattern Expansion remained relatively low gest that San Francisco Fig 3B left developed under topographic. over time but densification continued to rise sharply These trends are constraints allowing limited new development and creating notable. consistent with the widely held view of Atlanta as a sprawling metropol changes in density over the past 100 years Atlanta Figs 3B middle. itan region and the greater compactness of San Francisco in contrast had a massive increase in developed area since the 1960s. From these trajectories we can track the development of a city at and developed into one of the most sprawling cities in the United. fine temporal resolution over 200 years and visualize accompanying States with low building density Last the spatial patterns for Boston. spatial change patterns at the grid cell level By assessing the change Fig 3B right are illustrative of a city with an early developing and. SCIENCE ADVANCES RESEARCH ARTICLE 1 of 12 ENVIRONMENTAL STUDIES Two centuries of settlement and urban development in the United States Stefan Leyk1 2 3 Johannes H Uhl1 2 Dylan S Connor4 Anna E Braswell3 5 Nathan Mietkiewicz3 5 Jennifer K Balch1 3 5 Myron Gutmann2 6 Over the past 200 years the population of the United States grew more than 40 fold The resulting development of the

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