On the Harbor Charts, depth contours were used in tight coordination with
sanding. On most of the editions of NY40 and SF40, the sanding at 1, 2, and 3 fathoms
were continued with contours at 4 fathoms (NY40) or 5 and 6 fathoms (SF40). When
sanding was replaced by blue tint, contours were added at the same depths formerly
marked by the sanding to continue to provide detail on the overall shape of the bottom.
The two General Charts and the two Sailing Charts show substantial differences
between the east and west coasts in how contours were used for bottom representation.
The small-scale charts of the west coast, GJF200 and W1200, have very few depth
contours—only two depths are represented on the charts (except for W1200 1945/54). In
comparison, the small-scale charts of the east coast, MH400 and E1200, have from two to
nine different contours, averaging 5.4 for the 12 editions of the two charts. This
difference may be due to differences in landforms between the two coasts. The Pacific
coast is typically steeper along the shore than the Atlantic, which only gradually declines
along the continental shelf to the edge before dropping off. Having numerous contours to
represent the bottom would, along much of the west coast, create thick bands of lines that
individually provide little value to navigators, who primarily needs to know where the
shallows are. The gentle slopes of the continental shelf along the Atlantic are much more
amenable to multiple contour lines.
One of the most interesting set of editions to examine for the history of depth
contours are MH400 1938, 1942, and 1951. The clip for 1938 on Layout 06 shows a
single contour at 100 fathoms running north/south through both an area with many
soundings, and an area with few soundings. The 1942 edition has no additional soundings
on the chart, but in the area with many soundings, additional contours are present for 20,
30 ,40, 50, 500, and 1000 fathoms. The contours do not continue into the area with few
soundings. The 1951 edition shows the contours continuing into the area with few
soundings, but again no additional soundings are present.
Bathymetric contours were created by drawing a line of best fit through recorded
soundings. This practice was inherently less accurate than topographic contours because
the actual surface being drawn was not visible to the surveyor, unlike the land surface.
Few depth contours were present on early charts because few soundings were available,
and the level of confidence needed to draw in contours was not present. Additionally,
technology needed to make many soundings in very deep water was not available. Such
information was not needed to keep ships safe, and since most ships did not have the
equipment needed to make deep soundings, the information was unnecessary for
navigation, as well. An indication of this is that in the early years of the survey, the
C&GS referred to bathymetric contours as “Danger Curves”, focusing on their
importance for navigation in shallow water, not deep water (U.S. Treasury Department et
al. 1900a, 9).
As technology improved and deep soundings were more practical with the
invention of mechanical sounding machines, more soundings were taken in deep water.
Also, shallower areas were resurveyed and additional soundings were taken, filling in
knowledge about the bottom and allowing greater detail.
The echo sounder was a major advance in hydrographic surveying, leading to vast
increases in the amount of data the survey had available with which to compile charts.
Suggested as early as 1807, it was not until the Submarine Signal Co. tested a machine to
warn of icebergs (after the Titanic disaster) in 1914 and discovered return signals
showing the bottom of the sea that a working device was created (Theberge 1989). The
C&GS’s first use of a sonic depth finder was in 1923, and by 1928 all soundings in
waters over 15 fathoms were being taken with such devices (U.S. Department of
Commerce et al. 1923, 1928b; Theberge 1989). By 1939 the survey was using recording
echo sounders to collect 200 times as many soundings in a given period of time as could
be done in deep water using mechanical methods (Kerr et al. 1982; Theberge 1989). A
shallow water sounding device, the Dorsey Fathometer, came into testing in 1935, and a
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refined version found wide use by 1937 (U.S. Department of Commerce et al. 1936b,
136; 1938, 138).
Even the echo sounder had limitations, however. Before the advent of multibeam
and side-scan sonar, echo sounders could only provide a trace of the bottom directly
under the survey vessel. Since the distance between survey tracks varied with the
perceived threats posed by the hydrography of the area being surveyed, wide tracks could
still let navigational hazards go undiscovered (Craig 1996).
The best soundings are of no value in charting unless the location of the survey
vessel is known. Advances in positioning were just as dramatic and important as
advances in sounding. Before the advent of electronic positioning aids, soundings taken
out of sight of land were located using dead reckoning (Shalowitz 1957). The C&GS was
a leader in developing the technique of ‘radio acoustic ranging’ (RAR) in the 1920s. With
RAR, an explosive device was tossed into the water, and the sound of the explosion
would travel through the water to distant hydrophones connected to wireless transmitters.
Upon picking up the explosion, these units would transmit a radio signal back to the ship.
The differential timing of radio signals received on the ship from multiple hydrophones
allowed a triangulation calculation to locate the ship at the time of the explosion. This
technique was used until more advanced, fully electronic positioning systems were
developed during WWII.
A major innovation for the C&GS came in March 1939 with the publication of a
new edition of Chart 5101, designated 5101A (U.S. Department of Commerce et al. 1940,
99; Shalowitz 1964). It marked the beginning of a new role for bathymetric contours. It
was the first chart designed for ships that have their own echo-sounders on board.
Recording echo sounders allowed the survey to collect orders of magnitude more
information about landforms at the bottom of water bodies. Continuing to place primary
responsibility for representing this information with the point data that soundings
represent did not do justice to the richness of the data now available. Instead of playing a
subsidiary role to the soundings on the chart, contours could now play the same role as
topographic contours, that of being the primary representation of the land surface. This
change in role can be seen in such chart editions as MH400 1938, 1942, and 1951, and
E1200 1927, 1938, and 1948. As these series progress, contours gain significant detail,
while soundings either remain as they were or, as in E1200 1948, are dramatically
Another feature of the charts that is useful for navigational purposes is the
characterization of the material that comprises the bottom at various locations. This
information has been present on the charts from the first, and is still present today. It is
relevant to navigation through the use of a sounding lead that picks up a sample of the
material from the bottom. Matching a distinctive material like black sand to a bottom-
surface description on a chart could help a lost ship determine its location, especially
when combined with depth soundings. Examples of bottom-surface descriptions can be
seen on Layouts 04, 05, and 06.
On NY40 1844 and 1845, bottom description text was in nearly plain text and did
not need an explanatory key. On Layout 04 examples include “Grey Sand” and “Gr.
Sand”. Layout 05 has “Gr.Sand & Br.Shells” and “Gr.Sand Y.Specks” in addition
“Sand”. Layout 06 shows “Fine Grey Sand” and “Black & White Sand”. The text is
formatted as title case, in italics with serifs, and is the same size as the soundings. NY40
1853 has no bottom description text, and is the only chart seen here without.
In the second time period, the other charts began to see standardized abbreviations
for the bottom description text. Somewhere on the map, a note would be placed as a key
to the abbreviations. See Figure 4 for an example of this key from GJF200 1862. It
categorizes the descriptors as ‘Materials’, ‘Colors or Shades’, and ‘Other Qualities’.
Adjectives are divided into two categories by the practice of abbreviating Colors with
two letters and Other Qualities with three. The text in the key is in italics, as is the text on
Figure 4. Key to abbreviations, GJF200 1862
The abbreviations in the key apparently were specific to that chart so that codes
not used on the chart were not in the key. Another example of a key from the second time
period is shown in Figure 5, from E1200 1863. While the list of Materials is the same as
that on the key for GJF200 1862, the key for E1200 1863 has an additional four colors
and two qualifiers, ‘dark’ and ‘light’. It has two fewer Other Qualities listed, but includes
one not on the GJF list, ‘coarse’. The keys also have different headings, and only the
1863 version’s title is in all capital letters. It also has an additional note below the table
explaining how materials can be characterized as “principal” and “subsidiary”, apparently
meaning that both are present at a single location, but that one makes up a majority of the
Figure 5. Key to abbreviations, E1200 1863
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In the second time period, the size of the bottom description text on all of the
charts was decreased to be somewhat less than the size of the text for the soundings.
GJF200 1895 has an abbreviation key with the same format, as shown in Figure 6,
although the title has been shortened. Each column has one difference from the 1862
edition. ‘Rock’ is absent from Materials, but in Colors or Shades, the color “green” has
been added. In Other Qualities, ‘sticky’ has been replaced by ‘coarse.
Figure 6. Key to abbreviations, GJF200 1895
E1200 1900 has a major change in the key to abbreviations. Abbreviations are no
longer in a table but rather in a paragraph, and are placed under a single heading along
with other signs and abbreviations. Figure 7 shows the title and uppermost section of this
part of the notes, including all three of the categories of bottom description text. Each of
the three has more items listed than the 1863 edition. There are 11 types of materials, 8
colors (plus the two qualifiers), and 10 types of other qualities.
Figure 7. Key to abbreviations, E1200 1900.
This new strategy of moving the key from a table to just three lines was
eventually applied to other charts. MH400 1916, NY40 1917, W1200 1917/26, GJF200
1922, and SF40 1926 are the first editions where it is seen on the other charts.
Some examples of how the abbreviations are used on the charts include:
• Layout 6, NY40 1870: fne dk gy wh bk S
• Layout 6, SF40 1859/77: fne.S.M.
• Layout 6, E1200 1863: gy.&bk. S.rd.G.Sh.
• Layout 6, W1200 1855/64: M.
Abbreviations are mixed and matched to create a properly descriptive statement.
Sometimes all that is given is a single letter, while in other cases five or six abbreviations
are used. Primary material is described first, followed by secondary material.
In later time periods, changes were made to the form and even the content of the
bottom description text. First, the lettering was changed from serif to sans serif at the
when soundings were similarly changed, although the italics remained. Second, periods
were removed from each abbreviation at that same time. A third change between 1938
and 1940 was more significant. The list of abbreviations was standardized. Before this
change each chart had its own unique list of abbreviations, some quite long and using
possibly obscure or unclear terms such as ‘globigerina’, ‘ooze’, and ‘stiff’. After 1940
every chart uses the same, shorter, list of abbreviations, an example of which is shown in
Figure 8. Key to abbreviations, GJF200 1941/48
With the advent of electronic navigation systems such as Shoran taking primary
responsibility for determining the location ships even in poor visibility, and electronic
sounding devices to determine depth of the water even while underway, sounding leads
and knowledge of bottom composition became much less important navigational tools.
Bottom characteristics were not dropped completely, however, probably to provide
backup information should a ship lose all power and, therefore, all electronic navigational
aides. The information became less important and subsequently less prominent on the
During the 100 or so years covered by the study, soundings on the charts were the
primary method of communicating knowledge of the landform under the waters
described by the charts. It was not until the very end of this span of time that the burden
of primary communication was shifted to bathymetric contours, and even then soundings
remained on the chart to provide evidence for the validity of the contours. For all of this
responsibility, there are was very little change in the form of the representation of
soundings over this time. Soundings can be seen on Layouts 04, 05, 06, and 11. The
following descriptions are divided into a section on shoal water using Layout 04, and a
section on deeper water using Layout 06.
Soundings have been shown on the charts using three schemes of units of depth
1. Feet only
2. Feet and Fathoms
3. Fathoms only
Harbor Charts have mostly used feet as the unit measurement, but the mixture of
feet and fathoms is used on some editions during time periods two, three, and four.
General Charts used feet and fathoms during these same three time periods before being
converted to fathoms only. Sailing charts have only used fathoms only. Table 14 provides
a summary of the units of measurement used on each chart edition.
Table 14. Units of measurement for soundings
No significant differences in representation of soundings in shoal water are seen
between the different charts. NY40 will be described as the representative chart for
differences over time.
NY40 1844 has soundings in feet, and all of the numbers are integers. A close
examination shows that each numeral is unique, meaning that all of the numbers were
engraved by hand. There are places where the soundings are well-distributed, and other
places where they trace lines across an expanse that is otherwise free of soundings.
NY40 1845 has a note stating that “[t]he characteristic soundings only are given
on the maps. They are selected from the numerous soundings taken in the survey so as to
represent the figure of the bottom.” Indeed there are many fewer soundings shown on the
chart, and each proportionally covers a larger section of area (recall that this chart is at
1:80,000 while the 1844 version in six sheets is at 1:30,000). The lines of soundings are
not noticeable in the shallows. There are still irregularities in the letter forms, however.
As Table 14 shows, NY40 1853 has soundings in both feet and fathoms.
Soundings inside the danger line (18 feet) are in feet, while those in deeper water are in
fathoms. The soundings in feet are all whole numbers, while some of the fathom
soundings include fractions (¼ and ½ are appended to several soundings). Although the
scan is not the best, it does appear that the numbers are hand-engraved.
NY40 1870 has all soundings in feet. Fractions are added to some of the
soundings (¼ and ½).
No changes are apparent on NY40 1878 and 1902, but for 1914 the letter forms
are finally consistent enough to appear to be mechanically engraved. The fractional feet
are also gone.
The 1917 edition of NY40 is where a major change takes place for this chart: the
switch from serif to sans-serif letters for soundings. The look is cleaner, clearer, and more
modern. Less ink is used per numeral. The soundings appear to be chosen and placed
according to a grid system, and coverage is more regular than on previous charts.
NY40 1926 shows evidence of some re-survey work, with some additional
soundings in places, and other soundings removed. The result is a slightly less regular
distribution of soundings.
No changes are seen to the form of the soundings on NY40 1936 or 1944,
although small changes are made to the information based on later surveys.
NY40 1844 has a significant difference in the density of soundings between shoal
water and deeper water. A gradual tapering of density is seen moving away from the
channels through the entrance to the bay. Empty spaces begin to appear, which look to be
areas where soundings had not yet been taken.
NY40 1845 maintains the voids in deeper water seen on the 1844 edition.
On NY40 1853, individual lines of soundings appear to be represented. These
likely show where a hydrographic sounding crew made a single trip across an area,
recording soundings as they went. Sounding density dwindles to nothing in deeper water.
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