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UNEP-WCMC have developed a methodology to automate the process of merging terrestrial administrative boundaries (Global Administrative Unit Layers (GAUL), but can accommodate any terrestrial dataset) with VLIZ’s EEZ dataset, resulting in a contiguous territorial layer that has the potential to allow for consistent marine, coastal and terrestrial statistics across organisations. We have also integrated the latest, state-of-the-art global shoreline layer (to 30-metres resolution), which has improved the ability to delineate between marine and terrestrial regions.
We require a globally-consistent, high-resolution and regularly updated UN boundaries layer suitable for calculating terrestrial, marine and coastal statistics. The absence of this is leading to discrepancies in calculating and reporting on indicators across online platforms, making it difficult to establish shared, authoritative statistics. The ambition is that this layer can fill that void and link up analysis across platforms and organisations. Due to it being automated it will be easily updatable as the underlying datasets are updated.
The approached merged all three layers together while using the global shoreline layer as the source of truth as to whether a location was marine or terrestrial. Areas defined as marine were removed from the GAUL layer vice versa. Where gaps existed between the two layers an approach using thessian polygons were used to assign a "best approximation" or the approapriate territorial attribution based on the underlying layers. The script joining these layers can be accessed here.
The Underlying datasets:
GAUL: The Global Administrative Unit Layers (GAUL) is an initiative implemented by FAO within the Bill & Melinda Gates Foundation, Agricultural Market Information System (AMIS) and AfricaFertilizer.org projects.
The GAUL compiles and disseminates the best available information on administrative units for all the countries in the world, providing a contribution to the standardization of the spatial dataset representing administrative units. The GAUL always maintains global layers with a unified coding system at country, first (e.g. departments) and second administrative levels (e.g. districts). Where data is available, it provides layers on a country by country basis down to third, fourth and lowers levels. The overall methodology consists in a) collecting the best available data from most reliable sources, b) establishing validation periods of the geographic features (when possible), c) adding selected data to the global layer based on the last country boundaries map provided by the UN Cartographic Unit (UNCS), d) generating codes using GAUL Coding System and e) distribute data to the users.
Because GAUL works at global level, unsettled territories are reported. The approach of GAUL is to deal with these areas in such a way to preserve national integrity for all disputing countries (see TechnicalaspectsGAUL2015.pdf and G2015_DisputedAreas.dbf).
Exclusive Economic Zone (EEZ): Exclusive Economic Zones from the VLIZ Maritime Boundaries Geodatabase. Boundaries have been built using information about treaties between coastal countries. When treaties are not available, median lines have been calculated. An exclusive economic zone (EEZ) is a seazone extending from a state's coast or baseline over which the state has special rights over the exploration and use of marine resources. Generally a state's EEZ extends 200 nautical miles out from its coast, except where resulting points would be closer to another country. This dataset also contains delimitation of overlapping claims and joint regimes.
Global Shoreline dataset: A new 30-m spatial resolution global shoreline vector (GSV) was developed from annual composites of 2014 Landsat satellite imagery. The semi-automated classification of the imagery was accomplished by manual selection of training points representing water and non-water classes along the entire global coastline. Polygon topology was applied to the GSV, and the resulting polygons were mapped into four size classes of islands: Continental Mainlands, Big Islands (greater than 1 km2), Small Islands (less than or equal to 1 km2 and greater than or equal to 0.0036 km2), and Very Small Islands (less than 0.0036 km2).