Regarding to their scale, nautical maps are divided into two categories. Large scale charts and small scale charts. The map’s scale shows how many times a surface or a line of specific dimensions on the earth has been made smaller. This surface or line is depicted on the map. This means that the bigger the denominator, the more has been made smaller the depicted surface, e.g. 1:30000. On the other hand, the smaller the denominator, the less has been made smaller the surface of the map, e.g. 1:5000.

Therefore, a small scale chart is the one in which the depiction of the earth’s surface is very small, namely the linear value of the nautical mile is very small, e.g. 2mm. Small scale charts depict large surfaces and therefore contain few information concerning safety in navigation. These are the charts that depict oceans. The opposite happens with large scale maps.

a) General Sailing Charts. These are small scale charts that vary from 1/150000 to 1/600000. They depict large sea areas of the earth.

b) Coastal or navigation Charts. Their scale is bigger and varies from 1/50000 to 1/5000000. These maps depict smaller surfaces in comparison to geographical charts.

c) Harbor Plans. These charts, that are also called harbor charts, depict confined surfaces, e.g. a harbor with its entrance, small gulfs or anchoring bays, channels and river entrances. Their scale is smaller than 1/50000 and they are used during the approaching of the depicted area.

The nautical chart represents the navigable part of the earth’s surface on the sheet of the Mercator projection and provides all the useful nautical information. It is used by the mariner in order to sail safely between two points of the earth that are connected with a navigable surface, avoiding all natural and technical dangers of the area. The nautical map depicts both the part of the sea that connects the two points and the necessary part of the land close to the shores. Given that the nautical map provides all the necessary information about the sea’s surface (depths, reefs, islets etc) as well as about the shore (rocks, shallows close to the shore, lights etc), when at sea, it is the most important aid of the mariner. The importance of the map for the safety while sailing is that great that “a voyage without a map is inconceivable”.

Shape . The shape of the map is rectangular parallelogram. The vertical dimension of the height is oriented towards the North- South direction, while horizontal dimension of the breadth is oriented towards the east wind-west wind direction.

Dimensions . The map’s dimensions are given into centimeters or inches and are written into a parenthesis at the down right angle of the margin. This entry is necessary for the map’s inspection in cases of distortion because of permittance, humidity etc. Therefore, we see e.g. 630,0 X 980,0 mm or 8,43 X 25,49 inches. These dimensions refer to the sheer inner rectangular and they do not include the margin and the frame of the map.

Title of Chart . The title of chart defines the area that is depicted on it. If the chart is entitled “Crete island” the specific chart will depict Crete, its shores and the surrounding sea area. If Saronic Gulf is depicted on the chart, the represented area is the whole sea stretching of the Saronic Gulf, the islands that are located in it and the shores that are around it. Consequently, the title of chart forms part of its identity, concerning its identification. However, practically speaking, the term “title of chart” refers to the distinct frame, shaped as a rectangular parallelogram, inside the chart in which are placed:

a) The emblem and the trademark of the service that has published the map.

b) The wider area of which the chart forms part.

c) The depicted area in bold letters that in indexes is characterized as “title of chart”

d) The natural scale of the mercator’s projection of the chart is given for a specific breadth which usually is the average breadth of the chart, e.g. natural scale 1/125000 (at Lat 51 00’B).

e) Soundings in meters are counted by chart datum.

f) The heights. These are the heights of the lights, of rocks, mountains etc. The heights are described by the heights above mean high water spring or by the mean sea level. Therefore, in any case it is necessary to look the title of the chart.

g) The chart’s projection is a mercator’s projection.

Dates. In nautical charts some dates are inscribed that are very important for their accuracy, fidelity and update. The information referring to the age and the posterior situation of a chart are inscribed into obvious points in the following way:

a) First Edition. The chart’s first edition declares its age. This means that for a specific area it is the first time that a shores’ systematic marine surveying and a systematic sounding of the sea area takes place by the service that publishes the chart.

b) New Edition. If plenty corrections have occurred after the chart’s first edition, the chart is totally revised and modernized via a re-edition.

c) Reprinting. When the stock of a map runs down, the chart is reprinted with all the registered corrections. The previous edition does not annulated.

Symbols and Abbreviations. As previously stretched, the nautical chart, in order to respond to its purpose has to contain and depict clearly the information that stress the dangers and facilitate navigation. Given that these information are plenty and are presented in a great variety, they are rendered in the map with specific symbols and abbreviations. For the safety of the voyage and the exploitation of the given information, the mariner should be able to comprehend and explain these symbols.

The symbols and abbreviations are explained via specialized charts called “symbols and abbreviations charts”, published by the states’ hydrographic services in charge. The symbols and abbreviations of these charts accord with the conventional symbols and abbreviations model table that was drafted according to the corresponding decree of the international hydrographic conference in 1952 published by the International Hydrographic Organization (IHO). Thereby, there are no essential differences among the charts, symbols and abbreviations published by the IHO’s member states. The Hellenic edition (INT- 1), symbols and abbreviations table, includes all the symbols and abbreviations used in the Hellenic charts.

Chart’s Updates: The continuous updating of the charts with the new Notices to mariners published by Hydrographic Services is an indispensable prerequisite for their credibility.