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Ml1971)3211 Suggested Citation Ricketts TC, Savitz LA, GeslerWM, et al. Using geographic methods to understand health issues (AHCPR Pub. No. 97-N013). Rockville, MD: Agency for Health Care Policy and Research. (NTIS No. PB97-137707) Abstract Medical geography uses the concepts and techniques of geography to investigate health-related issues. This report aims to make the health services research community more aware of methods and approaches offered by the discipline ofgeography to the field ofhealth services research. With the computer programs and applications now available, it is possible to create maps and spatial interpretations that are not complex and do not require special data or systems. Data that apply to standard geographic areas can be mapped quickly and included in almost any type ofprinted report or visual medium. This publication leads the reader through several commonly used methods for producing maps and visual displays that can be used for policy analysis, research, and/or planning purposes. It incorporates demonstrations and interpretations ofapplications using real-world examples. The applications reflect both the disease ecology and spatial analysis aspects ofmedical geography. /VW1JD3Z GEOGRAPHIC METHODS Prepared for: Agency for Health Care Policy and Research Department ofHealth and Human Services U.S. Public Health Service 2101 East Jefferson Street MD Rockville, 20852 Grant Number HS0670(>-02 Prepared by: Thomas C. Ricketts, Ph.D. Lucy A. Savit/, Ph.D. Wilbert M. Cesler, Ph.D. Diana N. Osborne, B.A. University of North Carolina .it ( hapel Hill Table of Contents Overview 1 Methodology 2 Rural-Urban Continuum 3 Demographics and Access 6 Health Professions and Regionalization .... 10 Health Conditions 15 Conclusion 20 For Further Study 20 Technical Notes 21 Selected Software Manufacturers 22 The map, by some accounts, led authorities measures ofaccess, health care delivery, and to remove the pump handle during the 1854 resource allocation. These issues are Overview epidemic in London. particularly relevant to policymakers, health services researchers, and planners. Examples Maps are the basic tools that geographers This use ofmedical geography can be ofthese types ofstudies include: use to present information. Computers thought ofas diseaseecology, investigating have revolutionized mapmaking and placed the causes ofdiseases, and it has played an Studies of physician supply and geography at the forefront ofresearch. important role in many epidemiologic and demand by region or area. GeographicMethodsforHealth Services demographic studies. Medical geography Patient origin and geographic access Research, the book on which this also employs spatialanalysis, the study of studies. publication is based, is the result ofa the distribution ofdiscrete variables or multidisciplinary effort funded by the U.S. indicators. Small-area analyses that evaluate Agency for Health Care Policy and Research geographic variations m medical (AHCPR) to make the health services The three major types ofspatial analysis outcomes and practice patterns research community more aware of methods employed to understand geographical Marketing studies that analyze and approaches offered by the discipline of variation in disease frequency and/or health geographic variations in patient Hows geography to the field of health services status are: research. In a nontechnical formal, the Effective cartography and map interpretation authors introduce tools and techniques of Descriptive analyses ofthe distribution have been important elements in the medical geography that apply to health of disease. evolution ol modern medical geography services. Ecological or geographic correlation from both the disease ecology and spatial Medical geography uses the concepts and studies that seek to identify analysis perspectives. The widespread relationships between the distribution adoption of maps and other geographic to hniques ofgeography to investigate health related issues. Although some date of disease and some factor of interest. displays as analytic And decision-support such as lifestyle or environmental tools has been fueled rcccnllv by the tahlemofsiteld2,b5a0c0kyetaortsheagtoi,mtehoeltIeUrpmpomcedriacteasl exposure. increased availability ol software And geographyvvas firsi introduced by 18th and Migration studies that desi ribe databases for personal computers These 19th century physicians who attempted to differences in tin- geographic variation graphical displays cm be powerful tools that understand the relationship between the ofdisease lor populations, attempting reveal underlying relationships or processes occurrence <>l disease and environmental to separate geneti< effe< is from the Maps and 1 art< >graphi< analyses are conditions The most widely used example is environmental effe< is <>i pla< e appearing more often in health services John Snow s hand drawn dot map ol ( ases research journals and mimographs, and then or cholera (.1 water borne disease) Another focus ofmedical geography 1elates lllllll\ and ease (>| use ale deilloilstlaled concentrated around the- Broad street well. to the spatial analysis ol population based here Atlases and collections ofmaps relevant to made it possible to create maps and spatial (Topologically Integrated Geographic health are now available as reference interpretations. These computer programs Encoding and Referencing) file system. sources and as guides for policymaking. and applications are not complex, nor do TIGER incorporates most physical features of There are thousands ofdata sets that can be they require special data or systems to interest, including most streets and roads and used with hundreds ofcommercially produce excellent and informative maps. a wide array ofpolitical boundaries down to available mapping software programs. Given the widespread availability ofpersonal the smallest census divisions. The TIGER computers and the broad dissemination of files are often used as the source ofless This publication leads the reader through data in electronic formats, there is no reason complex sets ofboundaries. several commonly used methods for the why data that apply to standard geographic production ofmaps and visual displays that areas cannot be mapped quickly and The most common form ofcartography can be used for policy analysis, research, included in almost any type ofprinted report involves creating maps that represent spatial and/or planning purposes. By bridging the or visual medium. relationships as they appear from above the gap between the development and use of earth. However, certain distortions ofthe the tools and techniques ofgeography for Most maps depend on defined boundaries to physical relationship ofplaces may more health policy analysis, health services make them recognizable and meaningful. accurately represent the variables ofinterest research, and health care planning, this effort These boundaries include physical features, and their relationship to human perception. incorporates both demonstrations and such as coastlines or rivers, or political When a map is distorted to compensate for a interpretations ofapplications using real- boundaries, such as State and county lines. factor such as population density or travel world examples. These applications reflect Although drawing boundaries may seem time, the map is more accurately called a both the disease ecology and spatial analysis simple and fundamental to the lay user of cartogram. (Cartograms are presentations of aspects ofthe field ofmedical geography, maps, it comprises one ofthe more complex statistical data in diagrammatic form that depicting the utility ofthe analytic and tasks involved in computer mapping. resembles or relates to a map.) Many summary capabilities available to Boundary definitions make up most ofthe personal computer packages have the researchers, planners, and analysts. data involved in the creation ofa computer- capacity to produce cartograms that adjust drawn map, and the quality ofany map the size ofa place to a particular factor, such depends on the quality ofthe boundary data. as population. These distorted images Methodology require careful explanation for accurate Boundary files usually come packaged with interpretation because maps often reflect a mapping program, but they may be bought physical features. Mapping is part ofthe larger field of separately when special boundaries are of cartography (defined as the art, interest or to update changes in boundaries science, and technology ofmaking maps and such as ZIP Code areas. The U.S. Bureau of studying them), and has enjoyed a the Census produces and updates a complex resurgence in interest as computers have boundary set called the TIGER Rural-Urban Figure 1. Rural-Urban Continuum Categories: Minnesota, 1988 Continuum This map illustrates the application to One Minnesota of a 10- ofthe most vexing problems in tiered county-based health care delivery in the United States is how to provide an adequate and classification of rurality. The darker equitable level ofhealth care services to rural populations. Rurality is not a fixed and the shading, the simple concept; some would argue that rural more "rural" the and urban are the two ends ofa continuum county is. Continuum Code ofpatterns of human settlement, with — intermediate points along that continuum —largemetropolitancorecounties 1 largemetropolitanfringecounties defined by population density, distance from 2—mediummetropolitancounties — services, and the type ofeconomic activity 3 lessermetropolitancounties — cproenvtailneunutm,inoaneplaccaen. uTsoercehporreospelnetthtihcatmaps 456——nnnooonnnmmmeeetttrrrooopppooollliiitttaaannn,,,uulerrsbbsaannuiirzzbeeaddniaaznnedddanadonjndaacdaejdnjataccetenonttMtStooAMMSSAA trhuarailidtiyv.i(dIenpcohliotriocpallejtuhriicsdmicatpiso,nsabpyprdoepgrrieateeof 987———nnnooonnnmmmeeetttrrrooopppooollliiitttaaannn,,,ttlhheiisnnsllyyurppbooappnuuillzaaettdeeddanaadnnddnoanndoajndaajcdaejcnaetcnettnottMotSoMASMASA area shadings such as value, texture, and intensity are assigned to regions based on Note: MSAismetropolitanstatisticalarea. DataSource: AreaResourceFile,OfficeofDataAnalysisandManagement, BureauofHealthProfessions.March 1992. information collected prior to mapping.) Populations included in a county's borders Figure 1 illustrates one such system that contains a mix ol densely and more sparsely ma) relied a range ol age. gender, a\u\ race i lassifies counties using a system developed populated areas, with the largest distributions Mr- size ol the population that by the U.S. Department ofAgriculture. The concentration ol population Centered around is \i-r\ young or verj old has important rural-urban continuum < ode is based on Minneapolis St. Paul in the southeast unpinations lor the deliver) ol health both county population size and whether a quadrant ol the State mx.\ a smaller scmces \ count) wnh a large pediatric c OUnty is a core metropolitan county, some concentration surrounding l)iilnili in the population will require different specialists other type ol metropolitan county, adjacenl northeast quadrant. The variation in the size and services than will a count) that is made to or separated from a metropolitan county. and population density ol the counties up mostl) ofoldet people To characterize The' map shows thai the- State ol Minnesota illustrates the expected pattern ol settlement the- age distribution ol a county, one can use inmi tin- metn>p<ilitan < enters <»utwanI the piipulatii hi p) i.mud Figure 2. Population Pyramid: Brown County, Minnesota, 1990 The population pyramid shown in Figure 2 breaks population into 5-year age increments and divides it by gender, then graphs each increment using horizontal bars. This pyramid, which represents Brown County in Minnesota, shows 5-to-14-year-olds and people in their mid-twenties through thirties predominating, indicating that this county probably has a high proportion ofyoung families raising children. Population pyramids can also be used to examine other demographic variables ofinterest, such as race. Often, a problem or condition is widespread, % and its most important characteristic is the 3.4 2.6 1.7 0.9 0.9 1. degree to which it is distributed across MalePopulation 13,068 FemalePopulation 13,916 regions or concentrated in a single place. MaleMedianAge=33.3 FemaleMedianAge=35.7 Over the past 15 years, the number ofrural TotalPopulation26,984 MedianAge=34.5 hospitals that have had to close their doors has been recognized as a significant problem. DataSource: U.S.BureauoftheCensus. This population pyramid offers a Figure 3 provides a picture ofthe regional graphic depiction of nature ofthe phenomenon using a dot map. the age structure of In a dot map, point symbols are used to the population of show the spatial distribution ofsome feature Brown County, and give readers an idea ofits magnitude. Minnesota. The The relative concentration ofclosures in figure shows the Texas, Appalachia, and along the Mississippi population's age River is apparent. One broader interpretation distribution concen- that can be derived is that hospital closures trated in the 5-14 during this time period were primarily and 25-39 year age concentrated in the East and Midwest. The dot map, unless combined with some other groupings. shading, does not convey information about Figure 3. Rural Hospital Closures: 1980-90 A point map uses a dot or some other shape to indicate the feature of interest. In this map, each point represents a closed rural hospital. •Location of Closed Rural Hospital (N=315) DataSources:HospitalClosureFile 1980-89, HealthDatabaseServices.AmericanHospitalAssociation. HospitalClosure 1990dataset. OfficeofInspectorGeneral. U.S. DHHS. Construction of a the denominator (in this case, the total institutions, as well as conducting competitor Demographic Base Map number ofhospitals), and these maps must analyses. One way to analyze these patterns be interpreted carefully. is to calculate a commitment index, which A demographic base map alters the analyzes the proportion ofa hospital's representation ofactual spatial units (e.g., admissions deriving from each discrete Demographics counties) so the size ofthe unit is region within its service area. Commitment proportional to the numbers ofpeople or indexes are typically calculated at the county and Access resources living/located within its or ZIP Code level using hospital discharge boundaries. This is an important adjustment information. when the areal size ofselected spatial units From a geographical perspective, multiple varies disproportionately with the settlement Figure 5 is a choroplethic map that displays dimensions ofaccess to care can be patterns (or population density and the ZIP Code origins for patients admitted investigated among vulnerable dispersion) ofthese areas. during a set period. Shading is used to subpopulations residing in a given area. For identify a primary service area from which a — example, groups can be examined based on Figure 4 depicts an actual areal map of set proportion ofthe patients come in this rural or urban residence, low central North Carolina in the upper right case, those ZIP Code areas that contribute income/Medicaid coverage, race, ethnicity, corner, with the demographic base map the first 60 percent ofthe hospital's patients. age, gender, or transportation availability. reflecting the proportional differences in the To make this map, values were calculated These analyses can be compared against residential location ofthe population aged using a spreadsheet and the ZIP Code some societal norm or objective. However, 75 and over for an 11-county Health Service proportions were imported to a mapping typically internal comparisons are made that Area. Counties with proportionately smaller software program. highlight inequalities or patterns that can be land areas (such as Durham County) can visually assessed through map displays. become more prominent after adjusting for Population Potential Adjusting for population density is population density. Maps particularly important in conducting these types ofcartographic analyses. Patient Origin Method of Population potential is a measure of Medical Service Area distribution that describes the nearness or Examples ofthese types ofcartographic accessibility ofpeople to a certain point or Definition adjustments (included in this section) are place. The general formula for population demographic base maps (Figure 4), isoline Hospital planners are often interested in potential essentially calculates the degree of maps ofpopulation potential (Figure 6), and evaluating service areas and geographic interaction or the population potential for a two maps that relate access and sources ofadmission for patients. This point (typically representing an areal demographics using choroplethic and vector information can prove useful in planning centroid or geometric center). This point is mapping (Figures 5 and 7). community outreach or alliances of equal to the population ofthe area divided