<s>
A	O
flow	B-Application
map	I-Application
is	O
a	O
type	O
of	O
thematic	B-Application
map	I-Application
that	O
uses	O
linear	O
symbols	O
to	O
represent	O
movement	O
.	O
</s>
<s>
It	O
may	O
thus	O
be	O
considered	O
a	O
hybrid	O
of	O
a	O
map	O
and	O
a	O
flow	B-Application
diagram	I-Application
.	O
</s>
<s>
Some	O
cartographers	O
have	O
expanded	O
this	O
term	O
to	O
any	O
thematic	B-Application
map	I-Application
of	O
a	O
linear	O
network	O
,	O
while	O
others	O
restrict	O
its	O
use	O
to	O
maps	O
that	O
specifically	O
show	O
movement	O
of	O
some	O
kind	O
.	O
</s>
<s>
Many	O
flow	B-Application
maps	I-Application
use	O
line	O
width	O
proportional	O
to	O
the	O
amount	O
of	O
flow	O
,	O
making	O
them	O
similar	O
to	O
other	O
maps	O
that	O
use	O
proportional	O
size	O
,	O
including	O
cartograms	B-Application
(	O
altering	O
region	O
area	O
)	O
,	O
and	O
proportional	O
point	O
symbols	O
.	O
</s>
<s>
During	O
the	O
1850s	O
and	O
1860s	O
,	O
Minard	O
published	O
forty-two	O
flow	B-Application
maps	I-Application
on	O
a	O
wide	O
variety	O
of	O
topics	O
among	O
his	O
cartes	O
figuratives	O
.	O
</s>
<s>
During	O
the	O
1980s	O
,	O
Waldo	O
Tobler	O
conducted	O
experiments	O
to	O
create	O
flow	B-Application
maps	I-Application
by	O
computer	O
.	O
</s>
<s>
Early	O
computer-generated	O
maps	O
were	O
not	O
up	O
to	O
Minard	O
standards	O
,	O
but	O
Geographic	B-Application
information	I-Application
system	I-Application
(	O
GIS	B-Application
)	O
and	O
graphics	B-Application
software	I-Application
has	O
improved	O
in	O
the	O
ability	O
to	O
design	O
flow	B-Application
maps	I-Application
.	O
</s>
<s>
A	O
wide	O
variety	O
of	O
flow	B-Application
maps	I-Application
have	O
been	O
created	O
since	O
the	O
1830s	O
,	O
showing	O
movement	O
in	O
many	O
forms	O
.	O
</s>
<s>
According	O
to	O
Eduard	O
Imhof	O
,	O
a	O
flow	B-Application
map	I-Application
may	O
represent	O
several	O
different	O
aspects	O
of	O
the	O
phenomena	O
that	O
are	O
moving	O
and	O
the	O
networks	O
along	O
which	O
they	O
move	O
;	O
he	O
listed	O
the	O
following	O
:	O
</s>
<s>
Some	O
flow	B-Application
maps	I-Application
represent	O
flow	O
capacity	O
rather	O
than	O
actual	O
movement	O
volume	O
,	O
such	O
as	O
telecommunications	O
bandwidth	O
.	O
</s>
<s>
These	O
are	O
not	O
distinct	O
types	O
of	O
maps	O
;	O
a	O
flow	B-Application
map	I-Application
may	O
portray	O
any	O
of	O
all	O
of	O
these	O
aspects	O
simultaneously	O
.	O
</s>
<s>
The	O
types	O
of	O
phenomena	O
that	O
have	O
been	O
the	O
subject	O
of	O
flow	B-Application
maps	I-Application
are	O
varied	O
.	O
</s>
<s>
The	O
variance	O
of	O
flow	B-Application
maps	I-Application
in	O
subject	O
matter	O
,	O
and	O
the	O
relative	O
importance	O
of	O
Imhof	O
's	O
aspects	O
of	O
flow	O
,	O
has	O
led	O
to	O
a	O
number	O
of	O
design	O
strategies	O
.	O
</s>
<s>
In	O
a	O
1987	O
thesis	O
,	O
Mary	O
Parks	O
identified	O
several	O
distinct	O
types	O
of	O
flow	B-Application
maps	I-Application
,	O
which	O
has	O
been	O
widely	O
cited	O
although	O
her	O
list	O
was	O
not	O
comprehensive	O
and	O
more	O
are	O
included	O
here	O
.	O
</s>
<s>
In	O
a	O
distribution	B-Application
map	I-Application
,	O
paths	O
leave	O
the	O
origin	O
with	O
a	O
width	O
proportional	O
to	O
the	O
total	O
of	O
several	O
destinations	O
,	O
then	O
divide	O
as	O
routes	O
"	O
distribute	O
"	O
toward	O
each	O
destination	O
.	O
</s>
<s>
Designing	O
distribution	B-Application
maps	I-Application
requires	O
some	O
care	O
and	O
craft	O
in	O
drafting	O
the	O
flow	O
lines	O
so	O
they	O
divide	O
with	O
proper	O
widths	O
,	O
and	O
at	O
smooth	O
curving	O
angles	O
.	O
</s>
<s>
Computation	O
experiments	O
have	O
shown	O
the	O
potential	O
for	O
generating	O
these	O
automatically	O
,	O
but	O
today	O
most	O
are	O
drawn	O
semi-manually	O
using	O
GIS	B-Application
and	O
graphics	B-Application
software	I-Application
.	O
</s>
<s>
This	O
type	O
of	O
flow	B-Application
map	I-Application
originally	O
dates	O
back	O
to	O
the	O
Harness	O
map	O
of	O
Ireland	O
.	O
</s>
<s>
In	O
Imhof	O
's	O
list	O
above	O
,	O
a	O
map	O
that	O
visualizes	O
this	O
,	O
often	O
called	O
a	O
mass	O
flow	B-Application
map	I-Application
or	O
continuous	O
flow	B-Application
map	I-Application
,	O
focuses	O
on	O
direction	O
and	O
speed	O
of	O
flow	O
,	O
while	O
other	O
aspects	O
such	O
as	O
origin/destination	O
and	O
route	O
of	O
travel	O
are	O
largely	O
meaningless	O
.	O
</s>
<s>
These	O
can	O
be	O
readily	O
generated	O
by	O
computer	O
algorithms	O
,	O
especially	O
using	O
raster	B-Algorithm
GIS	B-Application
data	O
or	O
sample	O
point	O
data	O
(	O
e.g.	O
,	O
weather	O
stations	O
)	O
.	O
</s>
<s>
This	O
approach	O
is	O
more	O
akin	O
to	O
proportional	O
point	O
symbols	O
than	O
a	O
typical	O
flow	B-Application
map	I-Application
.	O
</s>
<s>
That	O
said	O
,	O
size	O
is	O
much	O
more	O
intuitive	O
for	O
total	O
amount	O
,	O
so	O
other	O
visual	O
variables	O
(	O
such	O
as	O
color	B-Language
hue	I-Language
or	O
color	O
value	O
)	O
may	O
also	O
be	O
considered	O
for	O
speed	O
.	O
</s>
<s>
Beside	O
the	O
flow	B-Application
maps	I-Application
in	O
cartography	O
there	O
are	O
several	O
other	O
methods	O
for	O
visualizing	O
non-geographic	O
flow	O
:	O
</s>
