Camera tow tracklines and navigation points are typically derived from acoustic transponder navigation collected at depth in a relative X-Y net. These positions are later put into geographic space through a multi-step process to provide the best geographic positions. See the metadata for each dataset for more specific information regarding accuracy. Separate GIS shapefiles for line and point topologies are provided.

Why two shapefiles for a single tow?
Data is stored within a GIS according to its topology. The particular GIS used for this project is vector-based and its objects are either points, lines or polygons. A dive track can be viewed as a line or a series of points. Point shapefiles contain each individual acoustic position and its attributes such as latitude, longitude and time. Line shapefiles depict the entire track and has attributes such as geographic place name location, vehicle, and length. Line shapefiles are particularily useful for locating all dives by year or making maps. Point shapefiles are better used for identifying a particular time or location on a given dive. GMT users should obtain the point shapefiles and use the *.dbf file after unzipping for use with psxy.