THE GIST OF                            MAP DATABASES                by Andrew Zolnai                           Geographic ...
figure), almost as lightly detailed and con-taining seven features, could be renderedon two sheets at 1:125,000.   Convers...
any map at any scale- This is the current       entered into this GIS. It is important to       Development Ltd. of Calgar...
together various townships (or portionsthereof) out of roughly 300 held on file.We can assemble them into target quad-rang...
Upcoming SlideShare
Loading in …5



Published on

My 2nd GIS paper in DOS days

Published in: Technology
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. THE GIST OF MAP DATABASES by Andrew Zolnai Geographic Information Systems (GIS) link graphic and information databases to produce new, up-to-date maps rapidly.H ave you ever noticed dragons, com- pass roses or inconsequent placenames peppering the large empty spaceson a map? The dragons and other fillersstem from our phobia for empty spaces.Meanwhile other areas of the map may bebarely legible for the crowded lettering ofimportant entries. This problem isparticularly acute in maps which have anintrinsically erratic distribution of data.Maps are traditionally kept on individualsheets in a variety of scales, and the in-formation displayed is a compromise be-tween abundant data and limited space. Any fixed format cripples map handlingif the information is complex, erraticallydistributed and rapidly evolving, as it isin the resource industries. In the north-ern oil business, for example, a new andcrucial mile-square territory may requirea map containing far more informationthan the maps for a thousand square milesof less prospective tundra. The informa-tion it holds may change with every seis-mic test result, and tomorrows choice oftesting site may depend on correct evalu-ation of yesterdays tests. With the shortseason and high costs of the Arctic, a map-ping system needs to adapt easily and de-liver fast. The trick is to devise a com-puter mapping system that allows mapmak- BEAD NICI JASON The monolithic map files were difficulters to edit and generate maps only as to maintain and took a long time to proc-needed, at a scale appropriate to the den- ess, and the systems themselves were More powerful microcomputer graph-sity of the data. hugely expensive. ics and software, now free from the bur- A Geographic Information System The next step was to apply to graphic den of handling huge files, have opened(GIS) provides a particularly flexible files the same principles of traditional da- up the field to affordable systems.means of storage and retrieval of graphic tabase management: storing the graphicdata, by coupling computer databases in- elements separately within an appropri-telligently with powerful graphic inter- ate framework, controlling file size, and Unit Area vs. Unit Densityfaces. The elements of a GIS include a providing links to combine the files in vari- Unit map area is typified by constant-graphic editor, a database management sys- ous ways. The individual graphic files are area map sheets all drawn to the sametem (DBMS), various input and output tagged with suitable locators such as grid scale—where, for example. 96 map sheetssystems, and some means to link these references or latitude/longitude to fa- representing one square mile might be re-together (fig. 1). cilitate combining them by machine. By quired to depict a twelve-by-eight mile re- linking individual elements into compos- gion at 1:50.000 (fig. 2a).Computer Mapping ite graphic files that remain manageable Unit data density suggests that if one- Early computer mapping systems coped in size and legible in output, one can then half of the region (the west side of fig.with myriads of points by using huge create maps of target areas and "zoom in" 2b] contains only four features of inter-graphic files on large mainframe systems. on areas of greatest density. est, a single map sheet at say 1:250.000 may be sufficient to portray it. Another area (the northeast quadrant of the same VOL 5 NO 2 CADalyst PAGE 24
  2. 2. figure), almost as lightly detailed and con-taining seven features, could be renderedon two sheets at 1:125,000. Conversely, if a single square mile iscrowded with sixteen features, dividingthat map into four separate sheets at1:10,000 will come closer to creating mapsheets of equal data density (ie. about fourfeatures per sheet). In this way manyfewer maps (30 sheets in this example),organized by unit data density, can be usedto contain the same information as the Figure 1: Synopsis of a GIS,96 sheets organized by unit map area. To link unit data density maps, a com-puter DBMS provides the obvious tool. der it fully. Thus a DBMS entry for aEach map sheet file requires a DBMS en- straight line might contain the locationtry to define its location, extents and scale. of its endpoints, its visual linetype (eg.The map sheet files may then be com- dashed) and a key to its nature (eg. prop-bined by a graphics program that can use erty boundary). A "symbol" entry mightthe DBMS entries to control the process. need only its symbol name and locationThe sheets can then be correctly placed coordinates; the graphics program rendersin relation to each other at the same scale. the symbols appearance from a single copyThe problem of text and symbol size in in its image library.combining files held at different scales With this approach, the problem of Figure 2: An eight-by-twelve mile regionmust be solved by the graphics program. scale can be eliminated. The actual geo- represented on maps of (a) Equal unit graphic data may be held at full scale, and area, and (b) Equal data density The dots is reduced automatically as needed by the suggest a typically uneven distribution ofGraphic Entities Database graphics program. Symbols and text must features of interest. Taking the principle of unit data den- be sized appropriately to some constantsity one step further, it is possible to make ratio to the sheet size, but this is also con- data density map sheets. The data reduc-greater reductions in the empty space, and veniently done by program as the sym- tion is so significant that they may sim-the data storage requirement, by convert- bols and lettering are generated. ply be held in a single uniform databaseing the graphic entities themselves into If in fact all the mapped territorys of moderate size. By linking this DBMSentries in a database file. Each entity re- graphic entities can be reduced to such to a suitable graphics engine, the requiredquires one entry with only the necessary DBMS entries, then it may no longer be graphic entities may be extracted from thedata to allow the graphics program to ren- necessary even to subdivide them by unit DBMS and used on demand to generateFigure 3: Video-tracing workstation. VOL 5 NO 2 CADalyst PAGE 25
  3. 3. any map at any scale- This is the current entered into this GIS. It is important to Development Ltd. of Calgary), and isState of GIS development. be able to digitize onto an existing grid, linked to a SUN 3/60 (at Software Sup- and to control imported data against that port Ltd of Calgary) to enlarge its GISAutoCAD and the GIS grid. Otherwise many an oil well is capacity. One implementation of such a GIS uses mapped on the wrong side of the road. This array of systems demonstrates thatAutoCAD as its graphics engine. Georef, Interactive editing capacities are desirable, map databases can be handled on widelyby Software Support Ltd. of Edmonton, as it helps to be able to compare original available and affordable microcomputers.Alberta, allows users to input and query hardcopies to digitized input rapidly. What can be read into such systems? In-data as AutoCAD drawing attributes, and Video-tracing systems accomplish such creasing amounts of digital data are avail-offload the attributes into a DBMS. This comparisons by projecting a video image able from commercial or governmentsystem permits users to convert or to ex- of the plotter-mounted hardcopy on an sources, or in-house as computerizationtract alphanumeric data as AutoCAD draw- AutoCAD screen (fig. 3), matching and evolves. The key to their proper use ising entities. The database link may be to synchronizing them via AutoLISP. Digi- to "high grade" such data, and to makea micro-based DBMS like R:Base System tizing is done by AutoCAD tracing and especially sure that maps are based on ac-V or Paradox, or the micro-to-mainframe drawing over the video. The interactive curate cadastral bases. ("Cadastral" refersuniform-structure database called Oracle. WYSIWYG process (pronounced Whiz- to property ownership boundaries.)Software Supports Munmap system, an zywig for "What you see is what you get")application package, is specific to the needs and the automatic quality control offered Some GIS Applicationsof municipal map users, who often have by image superimposition, both help to The Alberta Township System (ATS)their data already on a DBMS [see Mu- increase speed and accuracy over tablet is a comprehensive Universal Transversenicipal Mapping Made Affordable, p. 29}. digitization. Direct vector digitization by- Mercato(UTM)grid, recently resurveyedMy company customised this package fur- passes the raster-to-vector translation prob- and calculated, to which all other data canther to create Minmap and Oilmap for lems associated with scanners, and allows be referenced. It includes grid subdivisionthe resource industries. direct conversion into ASCII formats for and road allowance alignment. Software Much resource data is only available post-processing. Attributes can be entered Supports product Atsplot makes the ATSon map sheets. The only practical way to at the time of digitizing. The resulting data available now in an AutoCAD DXFenter this information into the database data may be easily extracted into RiBase format compressed and stored in underis to digitize it. In order to streamline the and merged with downloaded data. 10Mb. Cultural data may likewise beattribute input, we used a digitizing sys- For GIS hardware, we ourselves use an added at under 30Mb. An ATS grid withtem by Brighter Images of Lafayette CA, AT compatible for processing speed mid- road allowances, pipelines, road access,which synchronizes video and AutoCAD way between an inexpensive PC and the wells and morphology for one townshipgraphics for on-screen tracing of draw- powerful 386 machines. Control over file in the Pcmbina oilfield in Alberta formsings from an image of the original. sizes, through database management, can a roughly 180Kb drawing (fig. 4). Crucial in terms of volume and time allow large maps to be handled on 640K This GIS can produce a map with asspent is the consideration that many PCs if needed. Our particular machine can many layers as there are data types, bro-hardcopy documents in various forms (pa- be linked via Ethernet to a SUN 3/160 ken down into areas of coherent and man-per, mylar: maps, sections, etc.) must be network file server (at Teknica Resource ageable data density. It enables us to clipFigure 4: Screen photo of part of Pembina oilfield. VOL 5 NO 2 CADalyst PAGE 27
  4. 4. together various townships (or portionsthereof) out of roughly 300 held on file.We can assemble them into target quad-rangles with the desired layers of infor-mation. Any area of interest can be clippedout and worked upon, but coordinates re-main in that single UTM grid. The Geo-ref module allows us to import other datainto the AutoCAD maps, such as oilwelllocations or geophysical survey stations. Similarly, the province of British Co-lumbia makes historical mineral occur-rence data available to the industry onfloppy diskettes. Georef allows us to queryand input these data from R:Base intoAutoCAD. Oilmap and Minmap are othermodules that streamline the input of at-tribute data onto the maps withinAutoCAD, referenced to a UTM grid prov-ince-wide, or a property grid locally. Con-touring (using algorithms that grid, or tri-angulate, and map surfaces with commonproperties) can furthermore be performedfor volumetric resource assessment suchas oil, gas and mineral ore reserves. Another resource application concernsbore hole measurements, They reflectrock and mineral types underground, andused to be output as hardcopy logs, a wig-gly trace on a strip of paper. Once digi-tized as a polyline, these can be sampledby a LISP routine into files, and mergedwith more recent digital logs for con-touring. When done, the contour mapscan be re-entered into AutoCAD for over-posting correction, superimposition ontoan existing grid and possibly further digiti-zation of data not handled by contouringor other algorithms. These can be mergedwith other (eg. geochemical sampling) da-tabases to create comprehensive reportsand high quality maps.Tracks of the Dragon The challenge of computerized mappingis to enhance bulky hardcopy documentsinto a graphic database, to keep them up-to-date, and to create custom maps or sec-tions suitable for each purpose. The con-cept is to move from a map area unit toa data density unit. The answer is a pow-erful graphic engine coupled with a flex-ible database. The tool is a GIS to keepfiles manageable in size, amenable to smallsystem processing, yet capable of full CADand database management. Once, dragons may have roamed theempty spaces of ancient maps. Now, theprinciples of a GIS breathe fire into a newera of map management.Andrew Zolnai is a professional geologistand the owner of CAL-CAD Ltd. in Cal-gary, Alberta. CAL-CAD develops micro-computer based mapping systems. □