| A Base Map displays the fundamental data set (e.g. barangay boundaries, roads, schools, etc.) that is used to make sector data more meaningful. At a glance, a good Base Map should easily answer the question that we ask (“Where?”) when we look at a Base Map. A user should be able to relate the roads, landmarks and all other places and features found in the Base Map to the mental pictures he sees when a user looks at a map. Displaying or analyzing the base data with the sector data assists the user in making more effective and well-informed decisions.
The content of a Base Map depends on the user of the map and his intended use. The GIS Cookbook deals with the Base Map used for CLUP preparation and does not tackle the other base map as defined by other entities. The base map shall serve as a template for different mapping requirements where all other thematic maps may be overlaid for analysis. Thus, it shall aid the planners in coming up with the CLUP. It is important for the mapmaker and also the target custodians of these data to understand the procedural steps in the production of base maps, the hierarchy of the sources of data and some understanding about the data. This Chapter will deal with the concepts and generic procedures in preparing the GIS base map needed for CLUP. The following are the three major items to be discussed:
CLUP Base Map Features and Components The layout of the printed base map should have all the considerations and elements discussed in this chapter employed in its design. Both forms of the base map (digital and printed versions) should have the same features found, while the components will have a different form, and most will be found on both (North Arrow and tick Marks are usually not shown in the digital version). The components discussed in this chapter deals on how they should be in the printed form. Base Map Features |
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Table 1: Base Map Features
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Output CLUP Base Map Components An important output of the CLUP GIS is the output maps in printed form. This printed Base Map will be the form used and circulated more often than the digital format. It is important that the printed maps have a uniform format and appropriate contents to make them more useful for the user. Keys to Creating the CLUP Base Map First is to analyze the size and shape of the LGU in relation to the presentation format:
Elements of the Output Base Map The layout of the Base Map consists of the following elements (the numbers shown in red): 1 Legend 2 Reservations 3 Producer 4 Date of Printing 5 Map Window 6 Graticules and Tick Marks 7 Index Map Window 8 North Arrow, Scale, Datum and Projection
It has been observed that in most LGUs that have a working GIS, very few maps have been displayed. Besides being included in the document, there has been very limited distribution among stakeholders, as manifested by the absence of these maps in their offices. Though the data and large size printers are available, no maps are shown on walls of the municipal offices. This reveals the lack of appreciation and the will to disseminate these maps. In order to popularize the use of spatial information in planning, copies should be printed and displayed prominently on the walls. If the producer is concerned about the accuracy of the map or plan, the word ‘draft’ can always be applied. Steps in Preparing a GIS Base Map for CLUP
It is also recommended to use the Projection and Datum of the source during Georeferencing. Re-projection should be done on the digitized layer or output vector file. When combining different layers from these different sources, it will be noted that there will be discrepancies in dataset even if it pertains to the same features. Roads digitized from Cadastral Maps will not coincide with the same road taken from a NAMRIA Topomap, even if these layers were set to have the same projection and datum. If corrections or adjustments will be done either by the LGU or a consultant, documentation for the adjustments should be made and attached to the metadata. Any errors or discrepancies found on the source maps should be reported and consulted to concerned agency. The implementation of PRS 92 should also be considered when preparing the base map. LMB and NAMRIA, which are listed as the sources for administrative boundaries, are now implementing and converting their dataset into PRS 92. If the dataset for an LGU is already in PRS 92, they should ask assistance from Geodetic Engineers or concerned agencies like NAMRIA so that their other datasets can also be adjusted accordingly. Administrative Boundaries |
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Table 2: Hierarchy of Secondary Data type & Source
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| Capture Data from Technical Description/Coordinates Technical Descriptions of boundaries may be in the form of Line Bearing or Coordinate (Geographic or Grid). Data in this form may come from items 1, 2, or 3 of The Hierarchy of Secondary Data Type and Sources. These may be actual survey data for the boundaries or the ground coordinates for the boundary monuments. Positional values or coordinates of ground control points used in the map must be acquired from the LMB or DENR Regional office, if the data is in line-bearing form or local coordinate system. Any values in local coordinate system should be converted into grid coordinates. Request the boundary computations with points already given in plane coordinates. ![]() For Line Bearing/Coordinate For Line Bearing data, CAD software is popularly used but there are some GIS software that have utilities for capturing this type of data. Use the plotted version of the map if line bearing technical description is only accurate up to the nearest minute. Most line bearing TDs are rounded to the nearest minute and will not normally close. If only line bearing is available, do boundary computation and distribute the error of closure. If this is not possible seek assistance from the source agency to convert these into grid coordinates, or from a Geodetic Engineer to ensure that the correct procedure has been applied to the adjustments. Methods differ from software to software. Refer to toolbox…, for the example using GIS tools. For coordinate dataset, the following procedures should be followed:
Capture of Data from Paper Maps
Use of NAMRIA Topographic Paper Maps
Natural and Man-Made Features of the Base Map
Data Collection using GPS
Capture of Names Other Features Cadastral Maps Recommended Layout for the Output CLUP Base Map Steps in Securing Help for Preparing a GIS Base Map The following major steps are recommended in acquiring help:
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