STEP 15

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:

  1. Preparing the map;
  2. Photographing the 3D map;
  3. Digitizing and classifying the data;
  4. 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.

Figure 66: Grid stretched across a 3D map in Borongan, Philippines (JC Gaillard, August 2007)

Figure 66: Grid stretched across a 3D map in Borongan, Philippines (JC Gaillard, August 2007)

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).

Figure 67: Setting up a digital camera on a tripod before taking photographs of a 3D map in Dagupan,  Philippines (JC Gaillard, July 2009)

Figure 67: Setting up a digital camera on a tripod before taking photographs of a 3D map in Dagupan,
Philippines (JC Gaillard, July 2009)

Figure 68:  Photographing a 3D map in preparation for the integration of data into a GIS in Dagupan,  Philippines (JC Gaillard, July 2009)

Figure 68: Photographing a 3D map in preparation for the integration of data into a GIS in Dagupan, Philippines (JC Gaillard, July 2009)

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.

Figure 69:  GIS map extracted from a 3D map in Josefina, Philippines (Ecoweb, Inc.)

Figure 69: GIS map extracted from a 3D map in Josefina, Philippines (Ecoweb, Inc.)

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.

Advertisements

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s