1

Introduction to GIS

Jeff StoverDirector, Health Informatics & Integrated Surveillance Systems

Division of Disease PreventionVirginia Department of Health

EPID-600September 15, 2008

– GIS defined

– The geographic foundation for PH

– Public Health GIS history

• visualization

– Confidentiality

– GIS applicability to policy andpopulation health

– Data Quality Management

Overview

What is GIS?A geographic information system is an integrated

collection of computer software and data used toview and manage information about geographicplaces, analyze spatial relationships, and modelspatial processes.1

A computer-assisted system for the capture,storage, retrieval, analysis and display of spatialdata.2

Computer-based systems for integrating andanalyzing geographic data.3

1 A to Z GIS. ESRI Press.2 Clarke, 1986. p. 1753 Cromley and McLafferty. 2002

The Geographic Foundation forPublic Health

• Answers the basic question “where?”

– Where do people live?

– Where are the agents of disease or specifichealth-related events?

– Where can we intervene to eliminate/reducerisks or to improve health service delivery?

• People and the factors that cause diseaseare dispersed, often unevenly, acrosscommunities and regions.

Virginia Population Change

• http://vastudies.pwnet.org/pdf/va_time_line.pdf

• * US Census Bureau

1800 ~650,000

1900 1,854,184 +185%

2000 7,078,515 +282%

2007* 7,712,091 +8.95%

2

• http://www.cdc.gov/hiv/topics/surveillance/resources/slides/dot/slides/AIDSmaps.ppt

– Beginnings• 1970’s• Internal reports

– Late 1990’s• ODW

– OASIS• HIV/STD

– Office of Epidemiology• Fish advisories• Environmental Epi

– Enterprise GIS• EP&R

– Current status

GIS at VDH

Division of HIV/STD

3

• http://www.healthmap.org/en

Confidentiality

• GIS is fairly new to STD surveillance

• Technology has outpaced confidentiality standards

• Is geocoded and/or mapped data easily identifiable?– Use of rates, ranges, etc.

– Randomization of points, offsets

• Need to establish guidance for users and recipients– Data sharing agreements

“Mapping communicable diseases atdetailed geographic scales raisessignificant concerns about privacy andconfidentiality.”

Cromley and McLafferty, Guilford Press 2002.

• “CDC recommends that data bereleased in the form that is closest tomicrodata and that still preservesconfidentiality.”

CDC/ATSDR Policy on Releasing and Sharing Data

• “Protected Health Information…[means] any information,whether oral, written, electronic, visual, pictoral, physical,or any other form, that related to an individual’s past,present, or future…condition, treatment, services…whichreveals the identity of the individual…or where there is areasonable basis to believe such information could beutulized to reveal the identity of that individual….thisdefinition should be interpreted broadly.”

Model State Public Health Privacy Act

CDC Comments on Disclosure ofConfidential Information

“Those assessing the risk that confidential information willbe disclosed should recommend the statistical methodsto be used for disclosure protection (e.g. suppression,random perturbations, recoding, top- or bottom-coding.)The recommended methods should balance the risk ofdisclosure against the possibility that reducing the risk ofdisclosure will also reduce the usefulness of the data forpublic health practice and research.”

This requires staff trained to assess such risks.

4

From CDC Guidelines for HIV/AIDSSurveillance, Appendix C: Security and

Confidentiality

• “Geographic information systems (GIS) allow for relatively accuratedot-mapping. Care must be taken that graphic (like numeric)presentation of data cannot permit the identification of any individualby noting pinpoint observations of HIV cases at, for example, thecounty, ZIP code, or census tract level.”

• “Generally speaking, only aggregated HIV/AIDS surveillance datashould be released outside the HIV/AIDS surveillance unit throughpublished reports, grant applications, grant progress or planningreports, correspondence, newsletters, public meeting, or pressreleases.”

From CDC Guidelines for HIV/AIDSSurveillance, Appendix C: Security and

Confidentiality• “In developing a data release policy, state and local HIV/AIDS

surveillance programs should be mindful that, given the locationof a particular case-patient, less obvious data elements could belinked together to identify an individual. For example, whenreleasing data on a community with relatively few members of aracial/ethnic group or age group, surveillance staff should becareful that release of aggregate data on the distribution of HIV-infected individuals by these categories could not suggest theidentity of an individual.”

• “As a rule, CDC will not release aggregated data in tables whencell size is three or less (on a national level.)”

5

District: Fairfax

Reported: 50

A rollover on the districtshows the name and thereported number of cases

Note: A lower than normalreporting week would alsoappear on the map

6

Does GIS provide “added value”?

GIS is a tool for understandinghow spatial relationships canand/or do affect an outcome

[e.g., public health].

Is GIS more than just maps(“eye candy”)?

1. Available at:http://www.atsdr.cdc.gov/gis/conference98/gisindex.html

“As issues become visualized through maps,GIS can provide a mechanism to bring changeto communities.” 1

- Agency for Toxic Substances and Disease Registry (ASTDR)

1

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RR > 1, High Cluster ²

Spatial Scan (2000)Max. Cluster Size Set at 10% of Pop.

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Spatial and Temporal Scan (2000-2002)Max. Cluster Size Set at 10% of Pop.

Max Temp Cluster set at 1 year9,999 Replications

High Risk Areas (census tracts) were calculated. Hatchingshows census tracts with less than 1,500 people

7

Can GIS affect public health policyin a community?

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¯Billboard Analysis: Location of Billboards toHIV/AIDS Hotspots in Norfolk Area

8

Targeted Public Information Campaign based on GIS Analysis of Bus RoutesTraversing Core Areas

Can GIS affect change to the healthof a community?

Business Process Analysis

• How do we do our work?

• How should we do our work?

• How can an Information system[geocoder] support our work?

9

What is Geocoding?

Address:Address:920 Main St.920 Main St.Richmond, VA 23220Richmond, VA 23220

Longitude (X3):Longitude (X3): --77.45172377.451723Latitude (Y3):Latitude (Y3): 37.55016437.550164

905 Main St. X1, Y1910 Main St. X2, Y2920 Main St. X3, Y3930 Main St. X4, Y4940 Main St. X5, Y5

Street Database

Healthy People 2010:

Increase the proportion of all majornational, state, and local health datasystems that use geocoding to promotenationwide use of geographicinformation systems (GIS) at all levels.

John Snow

0139 Vibrio cholerae Dr.

Richmond, VA, 23231

Address:0139 Vibrio Cholerae Dr.Richmond, VA, 23231

Special Problem in Virginia

Solution: Geocoding

RichmondMorbidity

Henrico

Reporting Form

• Independent cities

• In Virginia, under state constitutional changesafter the American Civil War (1861-1865),beginning in 1871, cities became politicallyindependent of the counties. For many practicalpurposes, an independent city in Virginia sincethen has been comparable to a county. Manyagencies of the U.S. Government considerVirginia's independent cities to be county-equivalents.

http://en.wikipedia.org/wiki/Lost_counties%2C_cities%2C_and_towns_of_Virginia#Independent_cities

10

• Virginia is divided into independent cities and counties,which function in the same manner. According to the USCensus Bureau, independent cities are consideredcounty-equivalent.[58] Under Virginia law, allmunicipalities incorporated as cities are independent ofany county. As of 2006, thirty-nine of the forty-twoindependent cities in the United States are in Virginia.Virginia does not have any political subdivisions, such asvillages or townships, for areas of counties that are notwithin the boundaries of incorporated towns. There arehundreds of other unincorporated communities inVirginia, sometimes informally called towns.[59]

http://en.wikipedia.org/wiki/Virginia#Cities_and_towns

Name Street City County St Zip

A Movable Feast 1318 E Cary St Richmond Richmond City VA 23219

Azalea Food Market &Deli 211 Azalea Ave. Richmond Richmond City VA 23227

Blimpie 13969 Raised Anter Midlothian Richmond City VA 23112

Bogey's Bagels 13520 Midlothian Trnpk Midlothian Richmond City VA 23113

Boychiks Deli 4024-B Cox Rd Richmond Richmond City VA 23233

Café 1602 1602 Rolling Hill Dr Richmond Richmond City VA 23229

Carla'sKitchen 920 W Grace St Richmond Richmond City VA 23220

Street_new City_new St Zip_new Longitude Latitude Census Block FIPS County_new Code

1318 E CARY ST RICHMOND VA 23219-4155 -77.432889 37.53488751760030500

1095 51760 RICHMOND CITY S80 AS0

211 AZALEA AVE RICHMOND VA 23227-3621 -77.424351 37.60246351087200804

3000 51087 HENRICO S80 AS0

13969 RAISEDANTLER CIR MIDLOTHIAN VA 23112-2005 -77.663853 37.402642

510411010061024 51041 CHESTERFIELD S80 AS0

13520 MIDLOTHIANTPKE MIDLOTHIAN VA 23113-4214 -77.649450 37.503059

510411009151016 51041 CHESTERFIELD S80 AS0

4024-B COX RD RICHMOND VA 23233 -77.619700 37.624400 51087200115 51087 HENRICO E022ZC5X

1602 ROLLING HILLSDR RICHMOND VA 23229-5012 -77.546885 37.601315

510872001043022 51087 HENRICO S80 AS0

920 W GRACE ST RICHMOND VA 23220-4125 -77.451723 37.55016451760040300

1003 51760 RICHMOND CITY S80 AS0

11

-60%

-40%

-20%

0%

20%

40%

60%

2006 2005 2004 2003 2002

Richmond Henrico Chesterfield

* n = total number of net reassigned cases for the three jurisdictions

n* = 1074 n* = 859 n* = 1378 n* = 1443n* = 1568

METHODS developed by Harvard Geocoding Project

Association between poverty and reported HIV/AIDS,Chlamydia, Gonorrhea and Total Early Syphilis

Cases are quantified

CALCULATE AGE-STANDARDIZED

INCIDENCE RATESAND CONFIDENCEINTERVALS FOREACH POVERTY

LEVEL

CASESSTRATIFIED BY

POVERTY LEVEL

GEOCODINGHIV/AIDS CASES

AND STDS TOCENSUS TRACT

LEVEL

NUMBER OF CENSUS TRACTS BY POVERTYLEVEL*

0-4.9% below poverty

5.0-9.9% below poverty

10.0-19.9% below poverty

20.0-100% below poverty

* Percent below poverty based on US Census and conforms to federal definitions for poverty

12

Average annual age-standardized incidence rates forHIV/AIDS and STDs in Virginia (2000-2005), by poverty

level

Take Home Messages

GIS provides…• Improved analytic capacity• More accurate surveillance reports• Improved perception of data value• More efficient time and effort for data quality

corrections• More refined knowledge of localized activity• Improve assessment of public health

program/community needs• Greater understanding and rationale for targeted

public health efforts

Jeff Stover, MPH

Director, Health Informatics & Integrated Surveillance Systems

Division of Disease Prevention

Virginia Department of Health

Jeff.Stover@vdh.virginia.gov

Contact InfoHealth Informatics & Integrated

Surveillance Systems

- Excellence Matters -

improve program capacity throughenhancement and integration of

surveillance initiatives, data qualitymanagement, public health informatics

and epidemiologic research

Survey available @www.vdh.virginia.gov/epidemiology/DiseasePrevention/reportsandpubs.ht

m

Project Areas that Use GIS*Project Areas that Use GIS*

PhiladelphiaPhiladelphia

*Includes the following cities: Baltimore, Chicago, Los Angeles, San Francisco*Includes the following cities: Baltimore, Chicago, Los Angeles, San Francisco

BaltimoreBaltimore

ChicagoChicago

Los AngelesLos Angeles

San FranciscoSan Francisco

13

0%

10%

20%

30%

40%

50%

<1yr 1-2yrs 2-3yrs 3-4yrs >4yrs

GIS

Geocode

GIS/Geocoding

• Over half of the project areas (53%) use both GIS

& geocode

• Almost half of the project areas have used GIS andgeocoded for over 4 yrs.

Length of Time - GIS/Geocoded

* Time difference between use of GIS & Geocoding mainly due to project areas that use GIS butdon’t Geocode

GIS

• 27% use 2+ software applications for GIS– MapPoint, Street Atlas & QAS - used only in

conjunction with other GIS software applications

• Project areas not using ArcGIS - 3x morelikely to use >1 software program

Types of GIS Software Used

0%

20%

40%

60%

80%

ArcGIS SAS-GIS MapInfo EpiMap MapPoint StreetAtlas

Maptitude QAS Uknwn

22

65 1 1 1 11

6

Geocoding

• 90% of GIS users –geocode (3 do not)

• 54% of programs- STD only

0%

10%

20%

30%

40%

50%

60%

Geostan External

Vendor

MapInfo MapMarker Matchmaker StreetMap Other

Types of Geocoding Software Used

6

4 14

15

6

2

• 86% Mapping & Spatial Analyses

• 68% Mapping, Spatial Analyses & Target proginterv

Geocoding

0%

20%

40%

60%

80%

100%

Map Study

Disease

Spatial

Analyses

Address

Correct

Target

Interv

Other

26

8

25

6

20

1

How Geocoding is Used

Cell Suppression

• 56% use therule of 5

– Definition ofrule varied

• 1 project areadid not have arule

Numerator RuleRule

DefinedTotal # of

Project Areas%

Rule of 0 1 1 4%

Rule of 3 0-2 0 0%

1-2 2 8%

0-3 0 0%

1-3 0 0%

Total 2 8%

Rule of 5 0-5 4 16%

1-5 4 16%

1-4 5 20%

0-4 1 4%

Total 14 56%

Rule of 6 0-6 1 4%

Rule of 10 N/A 1 4%

Total # using a rule 19 76%

Other 5 20%

No Rule N/A 1 4%

Total Responded 25 100%

Confidentiality Guidelines

• 85% Indicated they did not havewritten guidelines that includedGIS/geocoding

• 75% Described unwrittenprocedures related toGIS/geocoding

• 13% Indicated in the process ofdeveloping

14

Obstacles to Use of GIS/Geocoding

0 % 15% 3 0 % 4 5%

Ot her

Insuf f .

st af f

Lack

t raining

GIS Geocoding

8

11

4

11

7

3

0% 15% 30% 45% 60% 75%

Not

priority

Insuff.

staff

No prog

need

Lack

training

Budget

1

1

1

1

2

• Use of GIS

– 55% would use GIS if training & technologyavail.

– 18% would like more info or were not sureif feasible/useful

• Use of Geocoding Data

– 67% (2) would geocode if training &technology avail

– 33% (1) not sure if useful

Obstacles to Use of GIS/Geocoding

Conclusions

• Use of GIS is increasing amongSTD programs

• GIS confidentiality guidance for STDprograms is needed

• More information on benefits of GISis needed

Geographic Distribution of Men Living with AIDS in 2001by U.S. Census Block Groups, San Francisco

15

Full suppression

No suppression

Numerator rule

Denominator rule

Denominator trigger numerator rule

"Small Counties"

Missing

County-level Suppression of AIDS (2003) Counts

Suppression here is defined as deletion of a table cell valueunder one of three categories of race/ethnicity (White, Black,Hispanic)

16

“Points, lines, and polygons”

“Grid, cells”

Two important representations of reality: Vector and Raster