ISSUES IN DEPICTING POPULATION CHANGE WITH DOT MAPS

Eugene Turner and James P. Allen, Cartography and Geographic Information Science, Vol. 37, No. 3, 2010, pp. 189-197

1. ISSUES IN DEPICTING POPULATION CHANGE
WITH DOT MAPS
Eugene Turner and James P. Allen

Cartography and Geographic Information Science, Vol. 37, No. 3, 2010, pp. 189-197
Trondheim, 30.11.2012 Martin KLÍCHA

2. WHICH KIND OF THE MAP BEST REPRESENT THE CHANGE ?

3. DOT MAPS


•Used to show distributions of
discrete phenomena.

•Each dot represents a
number of features.

•Can be overlaid on other
data.



Trondheim, 30.11.2012

4. USING DOT MAPS FOR POPULATION CHANGE


•Especially useful for showing population change between
census years.

Case study
•Describe the change in population in the Los Angeles County
by using Dot Maps.

•Census data 1990 and 2000.

•Dot size – 0.6 mm

•Dot value – 100 persons

5. PROBLEMS IN DOT MAPPING OF POPULATION
CHANGE


Change in census questions regarding race
•In census 1990 – people were forced to mark only one race
•In census 2000 – allowed to mark more than one race

•Census 2000 are not directly comparable to Census 1999.

•Solved by „bridging“ – reallocating the mixed-race responses to
single-race category.

•Used U.S. Census Public – Use Microdata Sample file for
California to determined for 1990 those persons who might
marked themselves as mixed-race in 2000.

6. PROBLEMS IN DOT MAPPING OF POPULATION
CHANGE


Change in tract boundaries
•Lots of boundaries between census data and tract was change.
•Non-matching tracts from 1990 have to be reallocated to
boundaries of 2000.

•Solved by overlaying other layers in ArcMap – street, park.

Change group quarters locations
•Shifting of some group quarters population
» non-housing units – prisons, hospitals, dormitories

•Special table form census was used to locate all places with large
group quarters populations.

7. CENSUS 2010


American Community survey
•Sent to 3 million addresses.
•Data released:
»every year for areas > 65 000 persons
»in 3-years for areas 20 000-65 000 persons
»in 5-years for areas < 20 000 persons



•American Community survey is the way how to have shorter
period between collection of „census“ data.

•The Census Bureau suggests to use five-years data instead of
mixing data from one or three and five-years samples.

8. CONCLUSION


•Dot maps capture detailed variations in population density.

•Very effective is when are used 2 different colors indicating gain
or loss in the population.

•Mapping population in this way is effective for getting a fell for
what is happening in different parts of a city and suburbs.

•Mapping change by different colored dots are easily understood
by people.