The total ozone maps are based on preliminary near-to-real time ground-based measurements received automatically at the WMO Ozone Mapping Centre and the. These include measurements from Brewer, Dobson, M-124 and SAOZ instruments. Total ozone values are given in Dobson Units. Maps of deviations represent total ozone deviations from the 1978-1988 level estimated using Total Ozone Mapping Spectrometer (TOMS) data.

Over areas with poor data coverage, depending on the period, adjustments are made according to TOMS on Nimbus-7, Meteor-3, ADEOS and Earth Probe satellites. Since 2005 in addition satellite measurements performed by OMI and SCIAMACHY sensors are used. Over the polar night area Dobson and Brewer moon observations and/or assimilated SCIAMACHY (TOSOMI) data are used courtesy of KNMI.

The mapping algorithm is similar to the one used by the World Ozone and Ultraviolet Radiation Data Centre. Data originators are invited to contact the WMO Ozone Mapping Centre and WOUDC if they wish to submit their data sets and participate in this project.

Since 1990 WMO has arranged for the preparation of daily maps of total ozone distribution over the Northern Hemisphere during the period 1 November to 31 March. This activity was requested by WMO Members. Since 2000 this service has been automated in collaboration with the World Ozone and Ultraviolet Radiation Data Centre and runs throughout the year.

The basis for these maps are ozone data obtained from about 100 monitoring stations of the WMO Global Ozone Observing System (GO3OS) which is now part of the WMO Global Atmosphere Watch (GAW) that are submitted in near-real time. Over the ocean areas these data are complimented by satellite data, TOMS in the past, SBUV-2 during winter-spring 1995-96, and currently TOMS on Earth Probe.

Since 2005 the site total ozone data from SCIAMACHY and OMI missions are also included in the operations of the Centre. The preparation and distribution of the maps is made by the WMO Northern Hemisphere Daily Ozone Mapping Centre operated by the Laboratory of Atmospheric Physics at the Aristotle University of Thessaloniki (Greece).