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

WHICH KIND OF THE MAP BEST REPRESENT THE CHANGE ?

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

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

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.

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.

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.

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.