Cruise Ship Overboard Discharge Project

To estimate general patterns of cruise line waste discharge in time and space, the Ocean Conservation and Tourism Alliance (OCTA) Science Panel requested data on discharges directly from the International Council of Cruise Lines (ICCL). The start and stop points for each discharge event were recorded in the database. It was assumed that each ship traveled in a straight line following the shortest-path distance on the globe during its time of discharge. For each pair of recorded start and stop points, a line feature was created in a gnomonic projection to produce an arc along the corresponding great circle for each point pair. These lines were then unprojected into decimal degrees for subsequent analysis.

To help eliminate data entry errors, modeled line segments that intersected any part of a land feature were eliminated from subsequent analyses. The coastline used for determining land features was NIMA’s VMap Level 0, a GIS dataset of base data features at 1:1,000,000 scale. To analyze geographic patterns in the distribution of waste, summary statistics were calculated using a 0.5-degree grid cell system. This returned the total count of lines per 0.5 x 0.5-degree cell for various subsets of the data.

Courtesy of Conservation International.