In spite of its lower accuracy this basic technique is still described because it can be of use to all those who cannot afford to purchase a high-resolution digital camera and where the relief of the model is limited. Supplies necessary for this operation include transparent plastic sheets, generally bought in rolls, overhead marker pens, scaled ruler, measuring tape, push pins, alcohol, cotton and one copy of the reference map. The plastic sheet needs to be cut to a manageable size (say 0.6-m x 0.6-m). Ahead of actual fieldwork, a grid matching the one on the base map needs to be drawn on each sheet using a permanent marker.

Extraction can start, provided the reference grid has been placed on the model. Location of the grid has to be accurate to limit any errors that may be made in transferring information from one medium to another. In this process the regular referral to the base map is helpful. Place the plastic sheets on top of the model.

At least three people are needed for a period of 2-3 days to extract information from a 6-7 m² model. Extraction should be done systematically. Points, lines and polygons are the three features representing the data. These should be separately transferred to the plastic sheets. Accurate documentation is essential. Attributes (non-graphic information like names, descriptions of land use and cover, demographic characteristics, etc.) are associated with single features. An ad-hoc legend is prepared for this. Those involved in extraction should bear in mind that the data transferred to the plastic sheets have to be digitized elsewhere. Therefore, information contained in the plastic sheets, accompanying annotations and legend must be understandable to other people as well. Despite the simplicity of the technology involved in transferring information from a 3-dimensional to a 2-dimensional medium, errors and distortions are inevitable. A major source of error originates from the perspective of the extractor when tracing information onto the plastic sheets. In order to limit distortions, the extractor should observe perpendicularly.

Taking pictures of the model still carrying the grid and the grid references limits errors. Enlarged prints may serve as visual reference during the tablet-digitizing phase. The transparent plastic sheets, accompanying legend and color prints are handed over to the GIS for digitization, editing, and data storage.

Information from official and other sources can be integrated (administrative boundaries, etc.). Attributes are ascribed to points, lines and polygons. The entire output is subjected to cartographic processing wherein colors, symbols and lines are chosen to represent the different attributes of the model. Customized thematic maps are produced at pre-determined scales.