STEP 15. INTEGRATING P3DM DATA INTO A GIS
15.1 P3DM, GIS and ethical concerns
Integrating data into a Geographic Information System (GIS) is an optional addon feature of P3DM for DRR which requires technical, most often external (to the community) expertise. It is applicable only when local knowledge may be thoughtfully integrated into larger DRR policies on the side of local authorities or NGO programs. In that case, it may be a powerful tool for broadcasting local resources beyond the local community.
Integrating P3DM data into a GIS requires that the skills, the hardware and the software and the resources for maintaining these in good shape are all available either in the community or within the hands of proximate outside stakeholder, e.g. local government or NGO. It is also possible that the NGO facilitator consider a GIS training component as part of a DRR project. In that case, it is recommended that great attention be given to the principles of Participatory GIS training as exposed on the IAPAD website: www.iapad.org
In any case, the use of GIS has to be carefully planned as it endangers local people’s ownership over their data. GIS data are indeed almost always manipulated beyond the community and there is therefore a danger that local knowledge is misinterpreted or transformed without the prior agreement of those who own the said data. Integrating P3DM data into GIS thus requires the highest ethics and dedication to participatory values.
15.2 Transferring data from the 3D map to the GIS database
The methodology for transferring data from the 3D map to the GIS database follows a simple four-step process, which includes:
- Preparing the map;
- Photographing the 3D map;
- Digitizing and classifying the data;
- Processing and valorizing the data.
15.2.1 Preparing the map
Before integrating P3DM data into a GIS, it is compulsory to set a rigorous grid of perpendicular yarns stretched at equal distance across the map as described in step 12 (Figure 66). This is essential to provide references for eventually georeferencing each photograph to be taken and digitized in the GIS. It is obviously similarly important to know the exact location in latitude, longitude and elevation of each corner of the 3D map and hopefully of a few more landmarks.
15.2.2 Photographing the 3D map
Photographing the 3D map is the most difficult part of the process as it must avoid any distortions between the actual map and the digital data. The reference Participatory GIS manual by Rambaldi Callosa-Tarr (2002) recommends the Parallel Camera Movement shooting method.
This method consists of taking a series of photographs along a straight line traced on the floor at a constant distance from the 3D map. The map is titled to facilitate the process. A set square is required to respect a perfect perpendicularity between the 3D map and the floor.
The camera is eventually set on a tripod at a given distance from the 3D map. A plumb line is useful to make sure that the axis of the tripod is exactly aligned with the line traced on the floor (Figure 67). A level is also required to verify that the body of the camera is perfectly perpendicular to the floor. That way every photograph to be taken will be perpendicular to the 3D map. The initial height of the camera depends on the size of the map. Usually several series of photographs at different heights are necessary to cover the entire 3D map. It is important to ensure that there is a slight overlapbetween photographs to facilitate stitching afterwards (Figure 68).
15.2.3 Digitizing and classifying the data
The third step of the process for integrating P3DM data into a GIS consists of digitizing the photographs using any GIS software. Digitizing has to carefully respect the data plotted by the local community. The digitizer has to permanently refer to the legend of the 3D map which may be very long and complex.
At that time it is best for the digitizer to classify the data by respecting the categories provided in the legend and by sticking to the local knowledge and interpretation of those who built the map. It is recommended that different layers of information are generated for every section of the legend so that the manipulation of the GIS database is eventually easy.
Note that digitizing data from a 3D map is difficult if overlapping beads have been used to replace pushpins – unless they have been piled up from the largest, at the bottom, to the smallest, on top.
15.2.4 Classifying, processing and making use of the data
Once the data are integrated in the GIS database it is henceforth possible to integrate them with existing data produced by other stakeholders. In addition, it is also possible to juxtapose data from different neighboring 3D maps to form a large, for example municipal, depository of participatory data and local knowledge.
Such spatial databases advantageously replace satellite images which are usually very expensive (if updated) and often require additional skills to decipher, which are often absent in marginal and/or poor locations. In addition, GIS databases fueled by P3DM are easily updatable and do not require the purchase of any more digital data. If a farmer has decided to till a new crop and if the 3D map is updated shortly afterwards it just requires on the side of the authorities or NGO which manages the database to take a new set of photographs to update the GIS. Similarly if a pushpin is removed, relocated or replaced it is very easily transferable into the GIS without any additional cost.
Thematic maps may be produced out of the GIS to assist land-use or development planning through drawing upon people’s knowledge (Figure 69). Obviously, this requires the highest ethics on the side of the planners and actions require discussion and prior approval of those who own the data and are first concerned by the measures to be taken, i.e. members of the local community.
GIS databases are also useful to monitor the evolution of the data in the 3D map, an issue which is difficult to integrate into the actual map. Storing images and digitized versions of the 3D maps at different periods of time may be useful to understand past, current and future trends in hazards, vulnerabilities and capacities – trends which are important in planning for DRR.