Help & Resources

The goal of the Global Maritime Traffic Density Service (GMTDS) is to provide access to the most up-to-date marine traffic information by building on a foundation of collective data and knowledge, and leveraging access to cutting edge geo-analytics and massive computing power. To date, GMTDS has processed over 100 billion AIS messages spanning more than ten years of historical data from a variety of data providers, resulting in roughly 550 billion processed density values.

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GMTDS User Guide

The GMTDS dashboard was designed with ease of use in mind. For detailed information about controls, navigation and functionality, please download the GMTDS user guide.

Download GMTDS User Guide


What is AIS data?

Automated Identification System (AIS) data is a system for automatically tracking nautical vessels using transceivers and is primarily used for collision avoidance. The transceivers broadcast a variety of data including position, vessel type, draft, and many other fields of information. These broadcasted messages are then captured by space-based satellites or land-based antennas and transformed into a variety of messages that can be used for different purposes.

What are the sources of the Global Maritime Traffic AIS data?

Global Maritime Traffic is unique in that we combine multiple commercially available and open source AIS data repositories to process our analytics. Due to licensing restrictions, we can not directly comment on the specific sources of the AIS data.

How trustworthy is AIS data?

AIS messages have automated and human entered portions of the message. Typically, the positional location of the vast majority of AIS transponders is accurate. We put our location data through a processing methodology to remove bad data. Human entered data like ship type, draf, and navigation status may contain harder to detect errors. For example, Navigation Status was excluded as a filter type from GMTDS due to the large amount of errors in the reported AIS messages.

How do I cite the GMTDS service or data in an academic paper or on an external website?

Authorized downloads from GMTDS are subject to the terms of the Creative Commons Attribution 4.0 International Public License and shall be attributed to: Global Maritime Traffic Density Service (GTMDS) retrieved from, a service of MapLarge 2021 <>

How much AIS data is included in GMTDS?

There are roughly 100 billion AIS messages that were processed by GTMDS resulting in over 500 billion density raster cells being available for analysis. The GTMDS monthly densities start in April 2011 and continue through typically the past couple of months. New data is processed and added on a regular basis.

What is the underlying technology for GMTDS?

The GMTDS architecture is supported by the MapLarge Application Development Platform. There is an internal Spatial Data Infrastructure (SDI) which is responsible for processing the raw AIS data and generating the rasters. Then there is the external SDI which is where the final density rasters are hosted for community access. Additionally, using the MapLarge Application Development Platform, the GMTDS application was build using modular components.

What AIS messages are included in the Ship Type categories?

Ship Type Ship Type AIS Code Values
Cargo Ships 70-79
Fishing 30
Ice Breakers Hand Curated List of Named Icebreaker Vessels from this site:
Non-commercial Ships 34, 35, 51, 54, 55, 58, 59
Passenger Ships 36, 37, 60-69
Service Ships 31-33, 50, 52, 53
Tanker 80-89
All Others Ship types not specified above
Unknown No ship type value was provided in the data

How is the Ship Draft category determined?

Ship Draft is a reported attribute in the AIS message. We process this data exactly as it comes in for each AIS message broadcast.

How is the Loitering category determined?

Loitering is defined as a ship spending more than 6 hours within a 1km2 area. If that is determined to be true, then that density raster will be displayed on the map. This layer essentially shows areas where at least 1 vessel spend more than 6 hours in a small area.

GMTDS Release Notes


Added new features supporting Polar projections and timeline enhancements


Data updated through April 2022

Application Features

Polar Projections are now able to be rotated by clicking and dragging on the map. Users can click the Compass Arrow to change rotation modes

The Timeline now displays an Average number of hours per day for each month. This allows users to better understand overall collection changes over time

Users can turn map labels on or off

Export now supports multi-month downloads in animated .GIF format. GIFs are exported with the month and year in the upper left corner

Map location and bounds are able to be accessed from the URL when accessing GMTDS from


No Update


Stability fixes and WMS Updates


No Update

Application Features

Polar Projections now center appropriately when a user switches to them


Added GetLegendGraphic call to the WMS URL menu


This update includes enhancements to the overall user experience of GMTDS and includes self-service export for the first time.


Density Data is now available through February 2022

Application Features

Self Service Export is now available. Users are able to select an area of up to ~5M square kilometers and export a single month or upto 12 consecutive months of data. Export formats include .TIFF, GridFloat, NetCDF, and CSV.

The timeslider has been moved to the bottom of the screen along with the legend for simplification and readability. You can scroll left to right on the timeslider by using a mouse wheel up or down movement.

Filter and projection selections have been updated with easy to understand icons.

The opacity slider has been made more clear and compact.


Updated the WMS URL information box to include GetMap, GetCapabilities, and GetFeatureInfo calls.

Added in WMTS Tile and GetCapabilities calls.


This is the first public release of the GMTDS data and application. This release serves as the initial baseline for the community to leverage.


Density Data has been processed from April 2011 through November 2021
Map hovers reflect Monthly Hours per Sq. KM for each raster grid cell

Application Features

Legal Disclaimer Pop Up
Time slider enhancements and bug fixes
Animation controls updated
Date Range with Reset button
Projections supported include: EPSG:3857, EPSG:4326, EPSG:3995, and EPSG:3031
Vessel Density On/Off Toggle and Opacity Slider with Legend
Port On/Off Toggle and Opacity Slider
Ocean Depth Hovers On/Off Toggle
Filter By Column including: Ship Type, Draft, and Loitering
Measuring Tool Supported in All Projections
Contact Us Button
Info Button for additional help
WMS URL Button to generate the corresponding WMS Query (More information on WMS can be found at the Info Button link)
Light/Dark Basemaps w/ Precision and Accuracy enhancements

WMS Features

GMTDS Rasters can be accessed via Open Geospatial Consortium (OGC) Web Map Service (WMS)
Full Data Filtering via Cassandra Query Language (CQL)
Addition Information can be found in the GMTDS Technical Integration Guide on

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