How long is
Australia's coastline ?
At
first b l u s h t h e q u e s t i o n
seems eminently reasonable,
bu
t it is as o p e n - e n d e d as t h e
c l a s s i c a l ' h o w l o n g is a p i e c e
of
s t r i n g ? T h e a n s w e r to
b o t h is t h e s a m e : it all
depends.
i n a c c u r a t e . F i n e w i r e (not
string) laid o n t h e d r a w n
coastline proved surprisingly
c o n s i s t e n t a n d a c c u r a t e (as
g o o d as dividers set to a
0 · 7 - k m interval) a n d so w a s
c h o s e n for t h e task. D o w n to
work.
D r R o b e r t G a l l o w a y of t h e
C S I R O D i v i s i o n of L a n d U s e
Research in Canberra was
recently confronted with the
question when compiling an
i n v e n t o r y of A u s t r a l i a ' s
coastal lands. L o o k i n g u p
published figures, h e found
th
e following answers:
Year Book of
Australia
Australian
W h e n the 162nd m a p was
p u t a s i d e , t h e total l e n g t h of
the mainland coast plus
T a s m a n i a w o r k e d o u t to be
30 2 7 0 k m . A d d i n g o n t h e
l e n g t h of c o a s t of all t h e
i s l a n d s greater t h a n 12 h a ,
a b o u t 16 8 0 0 k m , gave a
g r a n d total of 4 7 0 7 0 k m .
36 7 3 5 k m
Encyclopaedia
19 658 k m
Australian
Handbook
19 3 2 0 k m
T h e great d i s p a r i t y h a s t o
do
with the precision with
w h i c h t h e m e a s u r e m e n t is
m a d e . T h e larger a n d m o r e
detailed the m a p , and the
m o r e finely t h e m e a s u r e m e n t
is
m a d e , the longer will be
th
e coastline. Ultimately one
could walk around the coast
itself w i t h a m e a s u r i n g stick,
bu
t t h e a n s w e r still d e p e n d s
on
whether you use
s e v e n - l e a g u e b o o t s or a m e t r e
rule.
A few p o i n t s of
m e t h o d o l o g y h a d to be
a g r e e d o n before t h e e x e r c i s e
could begin.
(It's a p h i l o s o p h i c a l p o i n t
whether the coastline tends
to
a n y l i m i t as p r e c i s i o n
i m p r o v e s . S o m e say it d o e s ,
o t h e r s not.)
H o w far u p e s t u a r i e s
s h o u l d t h e c o a s t l i n e be
t a k e n ? It w a s d e c i d e d t h a t all
i n l e t s w o u l d be arbitrarily
( b u t c o n s i s t e n t l y ) c u t off
whenever their mapped width
w a s less t h a n 1 k m . W i t h i n
S y d n e y H a r b o u r , for
example, Kirribilli Point was
j o i n e d to G a r d e n I s l a n d .
S t r a i t s less t h a n 1 k m w i d e
were ignored, treating the
i s l a n d as t h o u g h it w e r e p a r t
of t h e m a i n l a n d .
T o settle o n a r e l i a b l e ,
repeatable figure, D r
G a l l o w a y got t o g e t h e r 162
maps covering the Australian
c o a s t ( N a t m a p ' s 1:250 0 0 0
series) a n d e n l i s t e d t h e h e l p of
M
s M a r g o B a h r of t h e
Division.
I s l a n d s less t h a n 12 h a
were ignored. Measuring the
c o a s t l i n e of t h e 2 6 0 0 i s l a n d s
l a r g e r t h a n t h a t w o u l d be
tedious in the extreme.
Instead, a 16% sample was
t a k e n a n d a g r a p h of c o a s t
l e n g t h a g a i n s t area d r a w n .
T h i s plot gave a good
correlation, allowing island
c o a s t l i n e s to b e derived
s i m p l y from t h e i r area.
However, the ten largest
islands (including Tasmania)
w e r e , for a c c u r a c y , m e a s u r e d
directly. ( M a c q u a r i e I s l a n d
and Lord H o w e Island were
not included.)
Mangroves were regarded
as p a r t of t h e l a n d , w i t h t h e
coastline following their
s e a w a r d fringe; c h a n n e l s
between mangroves were
t r e a t e d as e s t u a r i e s . All c o r a l
reefs w e r e e x c l u d e d .
Finally came the question,
w h i c h tools to u s e : a p a i r of
dividers, a m a p m e a s u r i n g
w h e e l , or a l e n g t h of s t r i n g or
fine wire? O n a test r u n
dividers gave c o n s i s t e n t
r e s u l t s o n l y if t h e s a m e
starting point was used; the
w h e e l w a s rapid b u t
As a m a t t e r of i n t e r e s t , a n
u n d e t e r r e d by t h e i r prior
efforts, t h e t w o w o r k e r s
e x a m i n e d t h e effect of
different divider l e n g t h s o n
the measured coastline
length when using smaller
1:2 500 0 0 0 m a p s . As
expected, the apparent lengt
of t h e coast of t h e m a i n l a n d
d i m i n i s h e d steadily as t h e
divider l e n g t h w a s i n c r e a s e d
s h r i n k i n g to 10 8 3 0 k m at a
1000-km intercept.
A simple formula was
d e r i v e d t h a t l i n k e d coast
l e n g t h to t h e l e n g t h of t h e
measuring intercept. Using
t h i s f o r m u l a to e x t r a p o l a t e t
a divider l e n g t h of j u s t 1 m m
gave a l e n g t h of a b o u t
132 0 0 0 k m for t h e m a i n l a n
coast of A u s t r a l i a , r a t h e r
more than three times the
c i r c u m f e r e n c e of t h e e a r t h !
Andrew
Bell
W h a t i s t h e l e n g t h of t h e
A u s t r a l i a n coast? R . W .
Galloway and M.E. Bahr.
Australian
Geographer,
1979,14,244-7.
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