<s>
A	O
Sliver	B-Application
Polygon	I-Application
,	O
in	O
the	O
context	O
of	O
Geographic	B-Application
Information	I-Application
Systems	I-Application
(	O
GIS	B-Application
)	O
,	O
is	O
a	O
small	O
polygon	B-General_Concept
found	O
in	O
vector	O
data	O
that	O
is	O
an	O
artifact	O
of	O
error	O
rather	O
than	O
representing	O
a	O
real-world	O
feature	O
.	O
</s>
<s>
They	O
have	O
been	O
a	O
recognized	O
source	O
of	O
error	O
since	O
overlay	B-Application
was	O
first	O
invented	O
in	O
the	O
1970s	O
.	O
</s>
<s>
These	O
meaningless	O
polygons	B-General_Concept
were	O
recognized	O
early	O
in	O
the	O
development	O
of	O
GIS	B-Application
.	O
</s>
<s>
In	O
fact	O
,	O
in	O
1978	O
Michael	O
Goodchild	O
found	O
that	O
they	O
constituted	O
the	O
majority	O
of	O
all	O
polygons	B-General_Concept
in	O
some	O
operational	O
GIS	B-Application
.	O
</s>
<s>
Early	O
programs	O
for	O
performing	O
vector	B-Application
overlay	I-Application
,	O
such	O
as	O
WHIRLPOOL	O
,	O
developed	O
mechanisms	O
for	O
preventing	O
sliver	B-Application
polygons	I-Application
,	O
such	O
as	O
the	O
"	O
epsilon	O
filter	O
"	O
(	O
fuzzy	O
tolerance	O
)	O
In	O
recent	O
decades	O
,	O
most	O
of	O
the	O
focus	O
of	O
software	O
vendors	O
and	O
practitioners	O
has	O
been	O
on	O
improving	O
the	O
quality	O
of	O
GIS	B-Application
data	O
to	O
prevent	O
them	O
.	O
</s>
<s>
Sliver	B-Application
polygons	I-Application
are	O
typically	O
created	O
when	O
polygons	B-General_Concept
are	O
automatically	O
generated	O
from	O
lines	O
that	O
should	O
be	O
coincident	O
(	O
e.g.	O
,	O
an	O
international	O
boundary	O
following	O
a	O
river	O
de	O
jure	O
,	O
or	O
two	O
adjacent	O
counties	O
)	O
but	O
are	O
not	O
,	O
due	O
to	O
the	O
natural	O
discrepancies	O
that	O
arise	O
from	O
manual	O
or	O
automated	O
digitization	O
.	O
</s>
<s>
This	O
can	O
occur	O
when	O
a	O
single	O
layer	O
is	O
digitized	O
and	O
adjacent	O
polygons	B-General_Concept
are	O
traced	O
separately	O
,	O
or	O
during	O
vector	B-Application
overlay	I-Application
when	O
separate	O
polygon	B-General_Concept
layers	O
are	O
merged	O
.	O
</s>
<s>
The	O
editing	O
systems	O
in	O
most	O
GIS	B-Application
software	I-Application
provides	O
for	O
snapping	O
,	O
in	O
which	O
a	O
point	O
placed	O
near	O
an	O
existing	O
point	O
"	O
snaps	O
"	O
to	O
the	O
exact	O
same	O
coordinate	O
.	O
</s>
<s>
During	O
the	O
overlay	B-Application
process	O
,	O
the	O
preferred	O
mode	O
of	O
sliver	B-Application
polygon	I-Application
prevention	O
is	O
the	O
use	O
of	O
a	O
fuzzy	O
tolerance	O
,	O
which	O
is	O
sometimes	O
called	O
a	O
"	O
xy	O
tolerance	O
"	O
(	O
ArcGIS	O
)	O
or	O
"	O
snapping	O
threshold	O
"	O
(	O
GRASS	O
)	O
,	O
and	O
was	O
originally	O
called	O
an	O
"	O
epsilon	O
filter.	O
"	O
</s>
<s>
If	O
it	O
is	O
set	O
too	O
large	O
,	O
narrow	O
but	O
meaningful	O
polygons	B-General_Concept
(	O
e.g.	O
,	O
islands	O
in	O
a	O
river	O
)	O
can	O
be	O
collapsed	O
.	O
</s>
<s>
If	O
sliver	B-Application
polygons	I-Application
still	O
exist	O
in	O
a	O
dataset	O
,	O
they	O
may	O
be	O
removed	O
manually	O
or	O
automatically	O
.	O
</s>
<s>
Some	O
GIS	B-Application
systems	O
provide	O
a	O
tool	O
for	O
topological	O
verification	O
,	O
which	O
searches	O
for	O
topological	O
errors	O
in	O
a	O
data	O
set	O
(	O
sliver	B-Application
polygons	I-Application
being	O
one	O
among	O
many	O
potential	O
types	O
of	O
error	O
)	O
,	O
flagging	O
them	O
for	O
correction	O
.	O
</s>
<s>
One	O
option	O
is	O
to	O
attempt	O
to	O
remove	O
them	O
automatically	O
;	O
many	O
GIS	B-Application
systems	O
provide	O
a	O
tool	O
(	O
usually	O
called	O
Eliminate	O
)	O
that	O
finds	O
very	O
small	O
polygons	B-General_Concept
and	O
merges	O
them	O
into	O
one	O
of	O
the	O
adjacent	O
polygons	B-General_Concept
.	O
</s>
<s>
There	O
is	O
usually	O
a	O
parameter	O
to	O
pre-select	O
,	O
in	O
situations	O
where	O
there	O
is	O
more	O
than	O
one	O
adjacent	O
polygon	B-General_Concept
,	O
either	O
the	O
largest	O
adjacent	O
polygon	B-General_Concept
or	O
the	O
one	O
with	O
the	O
longest	O
common	O
boundary	O
.	O
</s>
