O IN
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SP Spatial Join
Calculating Number of Physician per Population
2 GIS in Health and Planning
2 01
1/ 2012 Spring
3/ Rutgers University
by Wansoo Im, Ph.D.

Download census tract 2000 file
-www.state.nj.us/dep/gis
Download Municipal boundaries
-https://njgin.state.nj.us
“doctor point location layer” (downlaod from Sakai )
Census tract map/Municipality boundaries
=>Add All Maps in Arc GIS

CENSUS TRACT : OPEN ATTRIBUTE TABLE
In order to see what kind of information it has

DOCTOR LOCATION LAYER : OPEN ATTRIBUTE TABLE
In order to see what kind of information it has

HOW TO JOIN LOCATIONAL DATA WITH DATA FROM
ANOTHER LAYER?
Based on the location, we will join doctor’s location into Census tract layer.

JOIN DOCTOR POINTS WITH CENSUS DATA LAYER

CLICK “DATA FROM ANOTHER LAYER BASED ON
SPATIAL LOCATION”

SELECT “THE LAYER(CENSUS TRACT)” WHICH YOU
WANT TO JOIN WITH DOCTOR LOCATION

SET THE DIRECTORY(LOCATION TO SAVE YOUR
SHAPEFILE) -> CLICK “SHAPEFILE”

OPEN ATTRIBUTE TABLE TO CHECK IF NEW
LAYER(DOCTOR CTR) IS SUCCESSFULLY JOINT
By opening attribute table, you can check if data from 2 original
layers(doctor points/census tract information) are included into a
newly-created shapefiles.

LOOK THROUGH DATA

EXCEL – PIVOT TABLE
Objectives :
We are going to export data from maps into dbf.
(dbf. File includes the information of table, therefore, all shapefiles
including data in the table have dbf. file)
Open dbf. File in Excel
By using Pivot table, we will calculate the number of doctors by each
census tract
(the number of doctors belonging to each census tract)

OPEN ATTRIBUTE TABLE OF DOC_CTR LAYER
Click the menu icon to export data from table.

EXPORT DATA “DBF. FORMAT FILE”

WHY WE EXPORT DATA FROM TABLE?
(DBF. FORMAT)
Originally Doc_CTR shapefile already has one dbf.file, however, if we
start to open it in the excel and modify, we can possibly affect the
original map data as the table is directly linked to a map.
Therefore, we would like to export data from the original table so as
to create new dbf. File(so to speak, “copy” dbf. file). In this way, we
can adjust data(by using a new dbf. File) in Excel regardless of
affecting original data in the map.

OPEN -> CLICK “ALL FILES”-> CLICK “DBF FILE”

OPEN IN EXCEL

WE CAN USE EXCEL FOR DATA CALCULATION!

THE NUMBER OF DOCTORS WITHIN EACH OF CENSUS
TRACT.
Number of doctors in each of census tract.
How do we calculate?

USE UNIQUE ID TO JOIN “INDIVIDUAL DOCTOR LOCATION” WITHIN
CENSUS TRACT
– “KEY” FIELD OR “STFID”
(CENSUS TRACT ID)
Why can’t we use Tract field? – Tract id is within County (Aggregate scale)

CLICK “INSERT” -> PIVOT TABLE

CLICK “PIVOT TABLE”

CLICK OK

THEN YOU WILL SEE THIS TABLE ;

DRAG “STFID” INTO ROW LABELS

DRAG “STFID” INTO VALUES

COPY THE TABLE

PASTE “VALUE” INTO NEW “SHEET”
Counting Case depending on variable that you
chose.
In this case, Fivot Table counts the number of
doctors depending on the Census Tract
Area(Assigned by unique ID).

CLEAN THE DATA – FIRST ROW SHOULD INDICATE
THE NAME OF FIELD

CLEAN THE DATA – DELETE LAST ROW ; TOTAL
NUMBER

CHANGE “SHEET” NAME INTO DATA
Name that you can remember
No space/No special characters
(Arc GIS cannot recognize)

SAVE EXCEL FILE AND CLOSE IT
BEFORE JOINING IN ARC GIS PROGRAM

CENSUS TRACT LAYER- OPEN ATTRIBUTE BEFORE
JOINING DATA

JOIN THE TABLE

JOIN ATTRIBUTE FROM A TABLE

SELECT THE FIELD TO JOIN “STFID”
(UNIQUE CENSUS TRACT ID)

CLICK EXCEL FILE YOU SAVED

CLICK THE “SHEET” THAT YOU SAVED NEW DATA
(NO.DOCTORS BY CENSUS TRACT)

SELECT THE FIELD(STFID) FROM “DATA SHEET”

CHECK ATTRIBUTE TABLE TO MAKE SURE IF TABLE IS
JOINT WELL
There are some null data because this census tract is statewide while
doctor location is located only within Middlesex county.

CALCULATE THE NUMBER OF DOCTORS PER
POPULATION WITHIN CENSUS TRACT
The number of doctor
The number of population
Let’s calculate doctors per population.

ADD A NEW FIELD

FIELD CALCULATION

ADD FIELD
10 digit/3decimal

CREATE NEW FIELD (FOR DOCTORS/POPULATION)
->RIGHT CLICK TO DO “FIELD CALCULATING”

FIELD CALCULATOR
But you will have 0 if denominator(total population2000=0) is 0
Select the data which population 2000 is more than 0
Use Field Calculator to use formula (number of
doctors/population*100)

2 WAYS FOR SELECTION
1. Select by Attribute
select the layer “census 2000”, and select the field “population2000”
put formula
Pop2000>0 ->click apply
2. Sorting Ascending in Attribute Table
Open Attribute table, sort the data regarding population 2000, and
select data which is more than 0 in population 2000 field.

EX1) SELECTION BY SORTING POPULATION

EX2) SELECTION BY MENU (SELECTING BY
ATTRIBUTE)
Make sure if Population(denominator) is 0 not

FIELD CALCULATOR

RATE CALCULATION
– WHY 1000? INSTEAD 100?

IF THERE’S NULL DATA => ERROR!!!
Population should be over 0 AND
Number of doctors shouldn’t be null data
Therefore, number of doctor is more than 0 and calculate it again
(Assume that if there’s doctor, population is over 0)

YOU WILL GET NO.DOCTORS PER POPULATION
PERCENTAGE IN NEW FIELD YOU CREATED.

OUTCOME

UNSELECT DATA

GO TO SYMBOLOGY AND MAP IT OUT!
The number of doctors per population

EXPORT MIDDLESEX MUNICIPALITY FROM CENSUS
TRACT

SELECT MUNICIPAL OF MIDDLESEX COUNTY

EXPORT MIDDLESEX COUNTY CENSUS TRACT
Field : Double click “County”
Click “Unique value
County= Middlesex county

CHANGE DECIMAL DEGEE IN LEGEND
-> CLICK “LABEL” AND “FORMAT LABEL” CHANGE DECIMAL
DEGREE.

EXPORT MUNICIPAL BOUNDARY SHAPEFILE.
County = Middle sex

EXPORT MIDDLESEX COUNTY BOUNDARY SHAPEFILE.