The old charts of the Atlantic indicated a danger 30 to 45 miles to the southwest of Cape St. Vincent. This danger was omitted from the charts about 1786 owing to lack of confirmation. Later, in 1813 and 1821, it was reported that vessels were lost or damaged by striking this rock. Soundings of over a thousand fathoms are now shown on the chart in this vicinity and the rock no longer appears. A comparison of a Pacific Ocean chart of about forty years ago with one of the present time (Fig. 19) illustrates in a striking manner how many doubtful dangers, or vigias, have gotten on the charts and how after laborious search many of them have now been removed. This condition was especially true of the Pacific, owing to the numerous reports of an indefinite nature from whaling ships, among whose captains there was a saying "that they do not care where their ship is, so long as there are plenty of whales in sight." [Illustration: FIG. 19. PORTION OF CHARTS OF 1869 AND 1903, OF THE PACIFIC OCEAN WEST OF THE HAWAIIAN ISLANDS, TO ILLUSTRATE THE REMOVAL OF DOUBTFUL DANGERS.] [Illustration: FIG. 20. PORTION OF CHART OF PONCE HARBOR, SCALE 1-20000, TO SHOW SELECTION OF SOUNDINGS FROM ORIGINAL SURVEY GIVEN BELOW.] [Illustration: FIG. 21. HYDROGRAPHIC SURVEY OF SAME PORTION OF PONCE HARBOR, REDUCED TO ONE-HALF SCALE OF ORIGINAL SHEET.] PREPARATION OF INFORMATION FOR CHARTS. #Chart schemes.# Before commencing the preparation of a chart it is necessary to arrange a definite scheme for it, and the usefulness of the chart will depend materially on this preliminary plan, in which must be outlined its scale, size, limits, and features to be represented. New charts have sometimes been prepared simply to fit the surveys as they progressed or to fill immediate or local requirements. It is, however, desirable that general plans for series or groups of charts be made, and with changing needs, information, and conditions it is sometimes necessary that existing schemes be modified. #Compilation of information.# Considerable work must usually be done to get the field records in shape for the published chart. The soundings must be plotted and the characteristic depths selected. Only a part of the soundings that are made can be shown on the original sheet and only a small part of these are used on the final chart. A selection is made showing the least soundings on shoals and bars, the channel depths, and the characteristic soundings in anchorages and other areas. The original surveys are generally made on a considerably larger scale than that on which the chart is published, in order that the soundings may be more thoroughly plotted. The sheets must then be reduced to the scale of publication, and this can conveniently be done by means of photography or with a pantograph.