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PNW Ecosystem Research Consortium64 PNW Ecosystem Research Consortium
0%
1%
2%
3%
4%
5%
6%
7%
8%femalemale
1930>75yr
1970>75yr
1990>75yr
0%
2%
4%
6%
8%
10%
193020-24yr
197060-64yr
199080-84yr
femalemale
Per
cent
of P
opul
atio
nP
erce
nt o
f Pop
ulat
ion
.62 .73
3.77
2.73
6.49
4.18
9.819.33
3.75 3.80
1.931.26
Figure 83. Population pyramid types. Demographers recognize three
prototypical pyramid structures, constrictive, expansive, and stationary.
All indicate conditions of the populations which comprise them. A con-
strictive pyramid has fewer people in the younger age categories, and has
been typical of U.S. populations as baby boom populations shift to more
conservative birth rates. An expansive pyramid represents greater num-
bers of people in the younger age categories, and is typical of many
developing countries where birth rates are high, but conditions are harsh,
and life expectancy is short. A stationary pyramid shows roughly equal
numbers of people in all age categories, with a tapering towards the
older age categories. Countries such as Sweden show stationary age
categories because of relatively low, constant birth rates, and a high
quality of life.73
MaleFemale
Percent of Population
MaleFemale
Percent of Population
MaleFemale
Percent of Population
Constrictive Expansive Stationary
Demography
The study of the characteristics of population (from Greek root demos
meaning people and graphos to make a line) can be complex. Population
pyramids are a useful tool for understanding the structure and composition of
populations because they graphically portray many aspects of a population,
such as sex ratios and age structure (Fig. 82).
Pyramids can give insight into trends in population over time by their
portrayal of the relative number of people in a particular cohort. For ex-
ample, the swell of population in the “baby boom” cohort, now in its forties
and fifties, is apparent in many of the county population pyramids, as is the
“echo” baby boom, now five to fifteen years of age. Demographers have di-
vided population pyramids into three prototypical types (Fig. 83). While
these prototypes are useful for general interpretation of conditions, knowl-
edge of specific characteristics of particular populations is also important as
they may significantly contribute to differences between counties.
The pyramids in Map 15 are based on the total population of the coun-
ties which intersect the area of the Willamette River Basin (WRB) in 1930,
Population Pyramids M. Richmond
1970, and 1990. These times have been chosen to help illustrate the change
in the structure of American society. They bracket important transitions in
demographic factors through time. Some of the bar widths in the pyramids
for 1930 were adjusted to reflect the difference in how the data were col-
lected for that year. The thicker bars represent age cohorts that are divided
into larger increments than the standard five-year increments shown in both
1970 and 1990.
Portions of all WRB counties except Linn and Marion lie outside of the
basin. For these counties, adjustment has not been made in the pyramids to
reflect the portion of their populations that reside within the basin, and be-
cause populations are distributed unevenly across a county, this may affect
the results. Also, note that the size of the pyramids does not account for dif-
ferences in population size between the counties, which can vary consider-
ably. This information for 1990 is summarized in Figure 84.
Given these considerations, at least three distinct forms can be seen in
the population pyramids of 1990 for the counties which intersect the WRB.
In Lincoln and Tillamook counties, which are predominantly outside of the
WRB, a double hour-glass form is apparent, attributable to the above men-
tioned baby boom and echo cohorts common to the United States as a whole.
A third, large, older cohort, attracted to these areas because of their retire-
ment amenities,72 is also apparent. Benton County shows a predominance of
people in the low to mid-twenties attending Oregon State University (OSU).
For comparison, consider Lane County with the University of Oregon. The
large student population is less apparent because of Lane County’s larger
overall population and more urban context. Most other counties fall into a
third, generally constrictive pyramid, indicating smaller numbers of people
in the younger ages.30
Most of the pyramids for the counties that intersect the WRB depict an
interesting phenomenon in the change of late survivorship over time. It is ap-
parent that in 1930 the age cohort of 75 and over is dominated by the male
population. In 1990 the late survivorship of the female population becomes
substantially greater than that of the males. This phenomenon is illustrated
for Lane County in Figure 85. The purple path shows this pattern of late sur-
vivorship while the green path traces the 20-24 age cohort of 1930 through
time to the 80-84 age cohort of 1990. One can apply this simple analysis to
any of the other counties using the population pyramids on the facing page.
Figure 84. 1990 county population by gender and total.
Figure 82. Anatomy of a population pyramid. The “percent of popula-
tion” is calculated by the number of people of one gender in one age
cohort relative to the total number of people of that gender in the popula-
tion. Summing the bars on both sides of the graph would yield the
percent of one age cohort.
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
85+80-8475-7970-7465-6960-6455-5950-54
0-45-9
10-1415-1920-2425-2930-3435-3940-4445-49
Percent of Population
Age cohorts are listeddown the center of the
pyramid, and aredivided into five-year
increments.
In the pyramid, the percent of females is displayed to the left, and the males to theright. While slightly more males are born in any given population, the number offemales surviving to older ages is greater than the number of surviving males.
Female Male
Percent of Population
Female Male
Percent of Population
Female Male
Percent of Population
85+80-8475-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
85+80-8475-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
1930 1970 1990
85+80-8475-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
Figure 85. Lane County population pyramids for 1930, 1970, and 1990, and gender ratios for the trajectories
Willamette River Basin Atlas
2nd Edition
65Willamette River Basin Atlas
HUMAN POPULATION
S
N
Counties
Multnomah
Polk
Female Male
Female Male
Female Male
Female Male
Female Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
Female Male
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
Female
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
Male
Female
85+
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
Female Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
MaleFemale
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
0%2%4%6%8%10%12%14%16% 2% 4% 6% 8% 10% 12% 14% 16%
MaleFemale
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
2%4%6%8%10%12%14%16%
Female
0% 2% 4% 6% 8% 10% 12% 14% 16%
Male
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
85 +
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
1990
Benton
Clackamas
Columbia
Douglas
Lane
Lincoln
Linn
Marion
Multnomah
Polk
Tillamook
Washington
Yamhill
19701930
Female Male
Percent of Population
85+80-8475-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-145-90-4
Map 15. Population Pyramids
Approximate Scale 1: 800000
74
