WORLD ATLAS OF CORAL REEFS
Scale and resolution
The scale of a map Is a measure of the reduction
of the size of features in their representation on
that map. Resolution Is a related term, but Is a
more direct measure of the detail shown on a map
and generally refers to the minimum size of an
object visible on a map, or the minimum distance
by which two objects must be separated for them
to appear as such. The characteristics portrayed
In the spatial representation of any natural system
are strongly related to scale and resolution, and
these need to be seriously considered both by
those responsible for the preparation of maps and
by the end-users. A number of problems can
arise, especially In the generation of statistics and
the comparison of maps drawn at different scales.
This IS Illustrated by attempts to measure
coastline length: the complexity (and hence the
length) of any coastline shown on a map is a
function of map resolution. In the Caribbean, for
example, maps of Individual islands frequently
show great detail, including tiny offshore rocks
and Islets. Regional maps, by contrast, may summarize complex coastlines Into a tew simple lines,
while world maps often leave out many Caribbean
Islands altogether Measuring the length of coastline of any Island from each of these maps would
clearly yield three very different results.
With traditional photography the resolution
or level of detail can be altered by varying the
lens and photographic material, or by altering
the height at which images are taken, although a
balance must be struck between the area covered
by the Image and the detail or resolution to be
found In the resulting Image. Optical scanners
gather light from a continuous grid of defined
blocks known as pixels. The sensor records, for
each pixel, the reflectance levels for those wavebands tor which It is tuned. The resolution Is
largely a function of pixel size which Is, in turn,
dependent on the optics of the sensor and the
height at which the images are taken (although
this cannot easily be varied for satellites!.
The problems posed by scale are not simply
those of statistics. Entire natural phenomena will
be hidden or exposed depending on the scales of
study. This is of particular relevance in the coastal
zone where many narrow linear features are likely
to be entirely lost at low resolutions.
This atlas provides examples of some
"problems" of scale. Many of the maps have basescales of 1:1 000 000 or lower At this scale 1
millimeter on the map represents 1 kilometer on
the ground, and It Is very difficult to see features
with a diameter of less than ^00-500 meters. Many
of the worlds coral reefs are fringing or patch
structures which are narrower than this. Drawn
strictly to scale, such features would not be visible
In many maps. In an effort to address this problem
the boundaries or lines marking the locations of
reefs have been slightly exaggerated to ensure
that they are clearly visible on the maps, although
this also has the effect of exaggerating apparent
reef area. This same problem can of course be
carried back to the source materials (each of
which is listed for the particular maps! - source
materials prepared from remote imagery at
scales of 1 :1 000 000 will be unable to pick out the
smaller reef features.
detailed surveying expeditions led to levels of accuracy
which are quite extraordinary. Many of the sources used in
this atlas can be traced back, at least in part, to surveys
over 150 years old. In quite a number of cases such maps
have now been verified against air photographs and found
still to be highly accurate.
Remote sensing
Coral reefs largely occur in clear, shallow water. These
two factors make many reefs highly visible when observed
from above the ocean surface, and thus make them highly
amenable to being mapped using remote sensmg. Remote
sensing is the term widely applied for the "acquisition of
information about the land, sea and atmosphere by sensors located at some distance from the target of study".
Typically this means the gathering of images from aircraft
and satellites, although it also includes such techniques as
radar and, in the marine environment, sonar.
It was not long after aircraft became widely available
in the early 20th century that reefs began to be explored
and mapped from above. Vertical aerial photographs of the
Great Barrier Reef were first taken in 1925 and these same
images were used as a baseline for the survey by the Great
Barrier Reef Expedition of 1928-29. Great advances were
made in sonar technology during the Second World War
Scale and resolution
The scale of a map Is a measure of the reduction
of the size of features in their representation on
that map. Resolution Is a related term, but Is a
more direct measure of the detail shown on a map
and generally refers to the minimum size of an
object visible on a map, or the minimum distance
by which two objects must be separated for them
to appear as such. The characteristics portrayed
In the spatial representation of any natural system
are strongly related to scale and resolution, and
these need to be seriously considered both by
those responsible for the preparation of maps and
by the end-users. A number of problems can
arise, especially In the generation of statistics and
the comparison of maps drawn at different scales.
This IS Illustrated by attempts to measure
coastline length: the complexity (and hence the
length) of any coastline shown on a map is a
function of map resolution. In the Caribbean, for
example, maps of Individual islands frequently
show great detail, including tiny offshore rocks
and Islets. Regional maps, by contrast, may summarize complex coastlines Into a tew simple lines,
while world maps often leave out many Caribbean
Islands altogether Measuring the length of coastline of any Island from each of these maps would
clearly yield three very different results.
With traditional photography the resolution
or level of detail can be altered by varying the
lens and photographic material, or by altering
the height at which images are taken, although a
balance must be struck between the area covered
by the Image and the detail or resolution to be
found In the resulting Image. Optical scanners
gather light from a continuous grid of defined
blocks known as pixels. The sensor records, for
each pixel, the reflectance levels for those wavebands tor which It is tuned. The resolution Is
largely a function of pixel size which Is, in turn,
dependent on the optics of the sensor and the
height at which the images are taken (although
this cannot easily be varied for satellites!.
The problems posed by scale are not simply
those of statistics. Entire natural phenomena will
be hidden or exposed depending on the scales of
study. This is of particular relevance in the coastal
zone where many narrow linear features are likely
to be entirely lost at low resolutions.
This atlas provides examples of some
"problems" of scale. Many of the maps have basescales of 1:1 000 000 or lower At this scale 1
millimeter on the map represents 1 kilometer on
the ground, and It Is very difficult to see features
with a diameter of less than ^00-500 meters. Many
of the worlds coral reefs are fringing or patch
structures which are narrower than this. Drawn
strictly to scale, such features would not be visible
In many maps. In an effort to address this problem
the boundaries or lines marking the locations of
reefs have been slightly exaggerated to ensure
that they are clearly visible on the maps, although
this also has the effect of exaggerating apparent
reef area. This same problem can of course be
carried back to the source materials (each of
which is listed for the particular maps! - source
materials prepared from remote imagery at
scales of 1 :1 000 000 will be unable to pick out the
smaller reef features.
detailed surveying expeditions led to levels of accuracy
which are quite extraordinary. Many of the sources used in
this atlas can be traced back, at least in part, to surveys
over 150 years old. In quite a number of cases such maps
have now been verified against air photographs and found
still to be highly accurate.
Remote sensing
Coral reefs largely occur in clear, shallow water. These
two factors make many reefs highly visible when observed
from above the ocean surface, and thus make them highly
amenable to being mapped using remote sensmg. Remote
sensing is the term widely applied for the "acquisition of
information about the land, sea and atmosphere by sensors located at some distance from the target of study".
Typically this means the gathering of images from aircraft
and satellites, although it also includes such techniques as
radar and, in the marine environment, sonar.
It was not long after aircraft became widely available
in the early 20th century that reefs began to be explored
and mapped from above. Vertical aerial photographs of the
Great Barrier Reef were first taken in 1925 and these same
images were used as a baseline for the survey by the Great
Barrier Reef Expedition of 1928-29. Great advances were
made in sonar technology during the Second World War