<s>
A	O
nautical	B-Application
chart	I-Application
or	O
hydrographic	B-Application
chart	I-Application
is	O
a	O
graphic	O
representation	O
of	O
a	O
sea	O
region	O
or	O
water	O
body	O
and	O
adjacent	O
coasts	O
or	O
banks	O
.	O
</s>
<s>
Nautical	B-Application
charts	I-Application
are	O
essential	O
tools	O
for	O
marine	O
navigation	O
;	O
many	O
countries	O
require	O
vessels	O
,	O
especially	O
commercial	O
ships	O
,	O
to	O
carry	O
them	O
.	O
</s>
<s>
Nautical	O
charting	O
may	O
take	O
the	O
form	O
of	O
charts	O
printed	O
on	O
paper	O
(	O
raster	O
navigational	B-Application
charts	I-Application
)	O
or	O
computerized	O
electronic	B-Application
navigational	I-Application
charts	I-Application
.	O
</s>
<s>
Nautical	B-Application
charts	I-Application
are	O
based	O
on	O
hydrographic	O
surveys	O
and	O
bathymetric	O
surveys	O
.	O
</s>
<s>
Nautical	B-Application
charts	I-Application
are	O
issued	O
by	O
power	O
of	O
the	O
national	O
hydrographic	O
offices	O
in	O
many	O
countries	O
.	O
</s>
<s>
Every	O
producer	O
of	O
nautical	B-Application
charts	I-Application
also	O
provides	O
a	O
system	O
to	O
inform	O
mariners	O
of	O
changes	O
that	O
affect	O
the	O
chart	O
.	O
</s>
<s>
Various	O
and	O
diverse	O
methods	O
exist	O
for	O
the	O
correction	O
of	O
electronic	B-Application
navigational	I-Application
charts	I-Application
.	O
</s>
<s>
The	O
dramatic	O
accidental	O
discovery	O
of	O
the	O
Muirfield	O
Seamount	O
is	O
often	O
cited	O
as	O
an	O
example	O
of	O
limitations	O
in	O
the	O
vertical	O
geodetic	O
datum	O
accuracy	O
of	O
some	O
offshore	O
areas	O
as	O
represented	O
on	O
nautical	B-Application
charts	I-Application
,	O
especially	O
on	O
small-scale	O
charts	O
.	O
</s>
<s>
The	O
Mercator	O
projection	O
is	O
now	O
used	O
on	O
the	O
vast	O
majority	O
of	O
nautical	B-Application
charts	I-Application
.	O
</s>
<s>
On	O
nautical	B-Application
charts	I-Application
,	O
the	O
top	O
of	O
the	O
chart	O
is	O
always	O
true	O
north	O
,	O
rather	O
than	O
magnetic	O
north	O
,	O
towards	O
which	O
a	O
compass	O
points	O
.	O
</s>
<s>
Conventional	O
nautical	B-Application
charts	I-Application
are	O
printed	O
on	O
large	O
sheets	O
of	O
paper	O
at	O
a	O
variety	O
of	O
scales	O
.	O
</s>
<s>
Electronic	B-Application
navigational	I-Application
charts	I-Application
,	O
which	O
use	O
computer	O
software	O
and	O
electronic	O
databases	O
to	O
provide	O
navigation	O
information	O
,	O
can	O
augment	O
or	O
in	O
some	O
cases	O
replace	O
paper	O
charts	O
,	O
though	O
many	O
mariners	O
carry	O
paper	O
charts	O
as	O
a	O
backup	O
in	O
case	O
the	O
electronic	O
charting	O
system	O
fails	O
.	O
</s>
<s>
Nautical	B-Application
charts	I-Application
must	O
be	O
labeled	O
with	O
navigational	O
and	O
depth	O
information	O
.	O
</s>
<s>
There	O
are	O
a	O
few	O
commercial	O
software	O
packages	O
that	O
do	O
automatic	B-Application
label	I-Application
placement	I-Application
for	O
any	O
kind	O
of	O
map	O
or	O
chart	O
.	O
</s>
<s>
Other	O
symbols	O
show	O
the	O
position	O
and	O
characteristics	O
of	O
buoys	O
,	O
lights	O
,	O
lighthouses	B-Application
,	O
coastal	O
and	O
land	O
features	O
and	O
structures	O
that	O
are	O
useful	O
for	O
position	O
fixing	O
.	O
</s>
<s>
Older	O
charts	O
,	O
as	O
well	O
as	O
those	O
published	O
by	O
the	O
United	O
States	O
government	O
,	O
may	O
use	O
feet	O
or	O
fathoms	B-Algorithm
.	O
</s>
<s>
a	O
lighthouse	B-Application
,	O
are	O
generally	O
given	O
relative	O
to	O
mean	O
high	O
water	O
spring	O
(	O
MHWS	O
)	O
.	O
</s>
