5.10.02 Map Scales Projection

Thu, 11/15/2007 - 17:04
Introduction One of the activities of the Inter-Agency Task Force on Geographic Information (IATFGI) is to develop and recommend minimum standards for Geographic Information System interchange, and standard methodologies and concepts and definition for universal adoption by all government agencies in the generation of geographic information. The function/task of the IATFGI and its Technical Working Group are to come up with standards or at least an agreement with member agencies on the scales of maps and the type of map projection to be used by each agency. It was observed that when integrating and overlaying data from maps of different agencies, it was always a difficulty doing spatial analysis since most of the maps used are of different scales much more if the maps produced were compiled using different projections. With the availability of computer techniques to handle reducing and enlarging of maps, the above is not much of a problem these days. However, paper continues to play a role in modern mapmaking. Mapping institutions that have evolved from paper-based- to digital-based mapping face a dual problem; how to create new maps electronically, and how to convert existing maps into compatible electronic formats. Also, map related projects may involve a mixture of new electronic data as well as legacy data stored on paper, forcing the user to put together mapped information from different sources. Recommended Solution It is the intention of IATFGI to come up with agreed map scales to ease up overlaying procedures. The following table shows the map scales to be used both for central and local government as well as the private sector: Table 0 The scale of the map should permit representation of needed details with reasonable precision. The size or positioning of the smallest detail should fall within the allowable accuracy of the map (i.e. 0.2 mm for X and Y/planimetric coordinates at map scale at the smallest and thinnest line that can be plotted in the map, and 1/3 the contour interval in Z/elevation coordinates). As an example, a 1:10,000 map has an accuracy of 2.00 meters in X and Y ground coordinates and 3.00 meters in elevation (if contour interval is 10.00 meters). This means that a feature may have an allowable error of 2 meters in X and Y and 3 meters in Z from its exact position. Table 1 Map Projection In the production of the maps, the Transverse Mercator Projection shall be used except for maps at scales 1:1,500,000 which is in a Conical Projection where the reference latitude will be the equator (lat 0 ). The Universal Transverse Mercator (UTM) projection shall be used for all maps with scales smaller and equal to 1:10,000. To abide with the DENR Administrative Order No. 72-1 Series of 1990, a pair of Philippine Transverse Mercator (PTM) lines shall be shown on topographic maps to aid local surveyors and other users familiar with the use of the Philippines. Only the maps of PALAWAN at scales 1:250,000 shall use Zone 50 (117), the rest will be Zone 51 (123). Table 2 For maps on scales larger than 1:10,000, this system (PPCS) shall remain to be used. These maps shall follow the specifications stated in the Manual for Land Surveys in the Philippines (Lands Administrative Order No. 4 dated 3 July 1980). Table 3 In cases where it cannot be ascertain to which zone 1he map is to be projected or the area traverses two zones, then as a rule of thumb, the zone with the largest area will be the deciding or dominant zone is to be used. The assignment of provinces into the map projection zones of the PPCS shall be as follows: Exercises Compare recommendations with actual situation of the respective LGU Implication of the zone system for respective LGU
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