Land-sea boundary — Finistère department

The Land-Sea Limit is the astronomical high seas lead (PHMA) in the case of a 120 tide and under normal weather conditions (no wide wind and average atmospheric pressure of 1 013 hPa). The achievement of this geometric line is naturally defined as the intersection of a model of PHMA (extended to the coast and the estuaries) based on the available Bathyelli surfaces, and a numerical model of high-resolution coastal terrain. This limit, which also corresponds to the upper limit of the shoreline by materialising the top of the foreshore, takes into account, where they exist, the three administrative maritime boundaries: the Transverse Sea Limit (MCL), the Water Salt Limit (LSE) and the Maritime Affairs Limit (MAL). This limit is measured (rated) in relation to local hydrographic zeros as well as from altitude zero (IGN69 and IGN78 in Corsica). Attachment to other references (medium level, ellipsoid) is known. The Earth-Sea Limit product, derived mainly from the exploitation of the two products Litto3D®/RGEALTI® and Bathyelli, represents, at a metric resolution (1 to 5 metres), this theoretical entity by a set of 2D polylines describing the nature of the coast (artificial or natural, rocky or sandy, steep or low, etc.). The method of constructing the Land-Sea Limit allows the production of a continuous, homogeneous and spatially coherent boundary throughout the French metropolitan coastline. Use: In its planimetric dimension, the Earth-Sea Limit product is designed for analog use from the 1:2 000 scale; but it is imperative to consult the POSACC attribute (planimetric uncertainty) before any use on a very large scale. In its altimeter dimension, the user’s attention is drawn to the imperative need to consult the attribute VERACC (altimeter uncertainty combining the uncertainties of the MNT and PHMA). However, as the knowledge of PHMA is not exhaustive throughout the territory (i.e. rivers, lagoons, etc.), the 3 maritime administrative boundaries are identified (the “limarc” attribute at the passage of the Land-sea Limit) and used for closures. Attention, certain administrative maritime boundaries, although defined by decrees, present planimetric uncertainties of several hundred meters (commented in the attribute “descrp”). The product specification Land-sea limit also details the parties involved in the administrative maritime boundaries. The Land-Sea Limit is not intended to be used on scales higher than indicated. The Land-Sea Limit has not been designed to develop or inform indicators of coastal artificialisation; other approaches are taken within the framework of the Marine Strategy Framework Directive. However, due to its design identifying the natural and the artificial limit, it can contribute effectively to the result of completeness in this area. The Land-Sea Limit has not been designed for use in the operation of nuclear installations, air navigation or communication systems, air traffic control or navigation systems or any other area referred to as ‘dangerous activities’, where a product failure could result in death, bodily harm or serious physical or environmental damage. ©Shom-IGN Update: October 2021 This earth-sea limit replaces the coastline “HISTOLITT®” N_TCH_029 © IGN/SHOM 2009