The main aim of the Early Impact activities is to rapidly produce geo-referenced information on the impact of disasters, especially data on affected areas and population. The rapid mapping activities aimed at supporting the first stage of disaster management are generally based on satellite remote sensing data. Different types of satellite data can be used, mainly according to the type of disaster and the approximate extent of the affected areas:

• Low/medium resolution multispectral optical imagery (e.g.: MODIS, ALOS AVNIR, DMC, Landsat);
• High resolution optical data (e.g.: Spot, Formosat, Ikonos, WorldView-1 and 2; Quickbird, GeoEye);
• Medium resolution radar data (e.g.: Envisat, Radarsat, ALOS Palsar);
• High resolution radar data (e.g.: Cosmo-SkyMed, TerraSAR-X).

The aforementioned data belong to two main families: public-domain data (generally accessible through the web (e.g.: MODIS, Landsat); or commercial imagery that should be purchased through reseller companies (e.g.: Eurimage, Spotimage, DigitalGlobe). Sometimes it is possible to freely access satellite data on the basis of scientific agreements between Space Agencies and Principal Investigators in charge of a specific research (e.g.: ESA Category-1 users).

Very high resolution optical data are generally analysed to identify damages to buildings and infrastructures (road accessibility, collapsed bridges,...), landslides or temporary shelters. Unfortunately this kind of data are affected by the cloud coverage, that is often persistent during flood or cyclone events. The all-weather capability of the radar technology and the possibility to acquire data also during night time are crucial advantages of a radar based approach for the monitoring of those events.

The number and distribution of potentially affected populations is another important type of information requested by managers responsible for the distribution of humanitarian help. A rapid estimate of this information can be obtained by overlaying potentially affected areas with population distribution data.

The main outputs of an early-impact analysis are normally in the form of cartographic products covering the area of interest. Data should be represented following cartographic rules, both in relation to output map scale and according to representation rules.

The dissemination process has the same importance as the analysis and map production phases. Final products should reach decision makers at the right time and in the right place. Integration of map products with adequate metadata in a standard format is of great help during discovery and exploitation phases.