<s>
Map	B-Application
regression	I-Application
is	O
the	O
process	O
of	O
working	O
backwards	O
from	O
later	O
maps	O
to	O
earlier	O
maps	O
of	O
the	O
same	O
area	O
,	O
to	O
determine	O
change	O
or	O
to	O
locate	O
past	O
features	O
.	O
</s>
<s>
The	O
process	O
is	O
mainly	O
used	O
in	O
research	O
on	O
the	O
history	O
of	O
places	O
,	O
sometimes	O
termed	O
historic	O
map	B-Application
regression	I-Application
.	O
</s>
<s>
In	O
archaeology	O
,	O
map	B-Application
regression	I-Application
can	O
help	O
to	O
locate	O
features	O
appearing	O
only	O
on	O
earlier	O
maps	O
and	O
to	O
assign	O
building	O
phases	O
.	O
</s>
<s>
Map	B-Application
regression	I-Application
is	O
performed	O
either	O
by	O
comparing	O
individual	O
features	O
between	O
maps	O
,	O
or	O
by	O
re-projecting	O
an	O
entire	O
map	O
so	O
as	O
to	O
fit	O
another	O
onto	O
which	O
it	O
can	O
then	O
be	O
superimposed	O
.	O
</s>
<s>
Computer	O
based	O
geographical	B-Application
information	I-Application
systems	I-Application
facilitate	O
the	O
scaling	O
,	O
rotation	O
,	O
and	O
translation	O
of	O
an	O
entire	O
map	O
to	O
fit	O
over	O
another	O
.	O
</s>
<s>
Georeferencing	B-General_Concept
establishes	O
a	O
congruent	O
relationship	O
between	O
maps	O
,	O
and	O
allows	O
each	O
map	O
to	O
be	O
transformed	O
and	O
automatically	O
re-projected	O
as	O
an	O
overlay	O
.	O
</s>
<s>
This	O
method	O
is	O
useful	O
for	O
the	O
regression	O
of	O
maps	O
that	O
differ	O
in	O
format	O
,	O
for	O
example	O
,	O
raster	B-Algorithm
images	I-Algorithm
of	O
early	O
maps	O
and	O
vector	O
representations	O
of	O
modern	O
maps	O
.	O
</s>
<s>
Georeferencing	B-General_Concept
is	O
not	O
always	O
straightforward	O
;	O
topography	O
such	O
as	O
river	O
courses	O
and	O
coastlines	O
change	O
over	O
time	O
,	O
as	O
do	O
road	O
routes	O
and	O
other	O
built	O
structures	O
.	O
</s>
