Vol.1 No.2 2008

10/85

Research paper : Creation of seamless geological map of Japan at the scale of 1:200,000 and its distribution through the web (K. Wakita et al.)−79 Synthesiology - English edition Vol.1 No.2 (2008) original maps, it is very important to maintain positional accuracy. Therefore, GIS was employed actively in digital geological map where possible. After the attributes in neighboring maps were replaced with the unified legend, the areas of same geological divisions in both maps should share the attributes. However, it often happened that single geological body seemed discontinuous or different, because the information were independently compiled and published in different times. In such case, extra procedure as described below was necessary to maintain continuity.Generally, amount and accuracy of information in a map increase with time. In many cases, recent map contains more detailed and correct information of distribution of rocks or formations. In maintaining continuity of the boundary, the lines in old maps were altered to accommodate the lines in new maps. The latest geological information from the 1:50,000 geological maps or academic papers were employed to ensure better smoothing.Since old geological map is drawn according to old topographic map, superposing an old geological map on latest topographic map often caused slight positional mismatch. In such case, position of terraces or alluvial fans was corrected so it would be consistent with the latest topological data. Coastlines often posed more difficulties. Positional adjustment of island coast was accomplished using affine transformationTerm 8, by establishing several benchmarks. In other cases, geological boundaries were extended or shortened to match older data to the present coastlines using GIS.In addition to rock or formation boundaries, faults were reexamined to determine whether they were exposed or concealed based on latest research results. Specialists of the area and recent papers were consulted in making judgments on whether a geological boundary was a fault or not.4 From analog to digital, then from CD-ROM to the Internet4.1 The significance of digital geological mapGeological maps were generally printed on paper. Since the 1990s, with the development of GIS technology, social demand for digital geological maps increased. Therefore, we started to systematically examine the “publishing procedures by electronic media” in 1993, and published the first digital geological map on CD-ROMs in 1995. In contrast, seamless geological map has been distributed mainly on the Internet at present. The main reasons are: 1) it allows easier access to data and facilitates utilization, 2) it enables frequent data update, and 3) costless publication enables free (or low price) information provision. In 2006, there were 600,000 accesses to the Seamless Geological Map of Japan published in 2002, while sales of other printed maps were only about 900 copies a year. Although it is difficult to directly compare printed maps that are used repeatedly, three-digit difference is substantial. Moreover, wide range of users such as consulting firms and real estate companies, as well as researchers have accessed our website (Figure 7).4.2 Distribution on the webIn 2003, the National Institute of Advanced Industrial Science and Technology(AIST) started to offer seamless geological map on the web as one of research information database (RIO-DB, http://riodb02.ibase. aist.go.jp/db084/index.html). In the beginning, data were offered as images, although the original maps were created in vector format (Figure 8). Primary reason was because the public preferred to use maps in graphic form mainly to view and search and they were used to the printed version. Another reason was inadequate infrastructure for smooth browsing of vectorized data at that time.The total size of the current 1:200,000 Seamless Geological Fig. 5 Two types of the Seamless Geological Map of Japan 1:200,000. Basic Legend Version (left) and Detailed Legend Version (right).Fig. 6 Harmonization process for seamless geological map.Two adjacent mapsNew MapOld MapUnify the legendHarmonization of unit boundary Fit the polygon boundary Based on latest geological modelOriginal Geological MapSeamless Geological MapUniversity &Research institute38 %AIST16 %Civil engineering14 %Government & Agencies10 %Construction 6.1 %Industry3.6 %Local governments3.2 %Telecommunications2.9 %IT 2.5 %Resource & Recycling0.71 %Mass media 0.64 %Housing & Real estate 0.16 %Other 2.2 %430,000420,00070,00060,00050,00040,00030,00010,00020032004200520062007020,0002002Fig. 7 User category (left side, reference to November 2007) and change of number of access to the homepage of Seamless Geological Map of Japan 1:200,000 (right side, from September 2002 to November 2007).(7)−

※このページを正しく表示するにはFlashPlayer9以上が必要です