Table Of ContentMl1971)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
