u21-THE RASTER VECTOR DATABASE DEBATE

u21-THE RASTER VECTOR DATABASE DEBATE - UNIT 21 - THE...

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Sheet1 Page 1 UNIT 21 - THE RASTER/VECTOR DATABASE DEBATE <toc.html#UNIT21> UNIT 21 - THE RASTER/VECTOR DATABASE DEBATE Compiled with assistance from Charles Parson, Bemidji State University # A. INTRODUCTION <#SEC21.1> * Raster or vector <#SEC21.1.1> * Basic issues <#SEC21.1.2> # B. COORDINATE PRECISION <#SEC21.2> * Raster precision <#SEC21.2.1> * Location of coordinates in raster <#SEC21.2.2> * Vector precision <#SEC21.2.3> * Data precision <#SEC21.2.4> # C. SPEED OF COMPUTING <#SEC21.3> # D. MASS STORAGE <#SEC21.4> * Raster storage <#SEC21.4.1> * Vector storage <#SEC21.4.2> # E. CHARACTERISTICS OF PHENOMENA <#SEC21.5> * Raster sampling <#SEC21.5.1> * Vector sampling <#SEC21.5.2> * Features, entities and objects <#SEC21.5.3> # F. SUMMARY <#SEC21.6> * Combinations of raster and vector <#SEC21.6.1> # REFERENCES <#SEC21.7> # EXAM AND DISCUSSION QUESTIONS <#SEC21.8> # NOTES <#SEC21.9> This unit specifically addresses the issue of raster versus vector by looking at the different dimensions of the debate. We have tried to stress the importance and value of both models by comparing specific technical aspects. The next unit looks at a related but more abstract debate. UNIT 21 - THE RASTER/VECTOR DATABASE DEBATE Compiled with assistance from Charles Parson, Bemidji State University
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Page 2 A. INTRODUCTION <#OUT21.1> Raster or vector <#OUT21.1.1> * Unit 4 introduces definitions of raster and vector * arguments about which was better have been commonplace since the earliest systems were created * raster databases are appealing o simplicity of organization o speed of many operations, e.g. overlay, buffers o especially appealing to the remote sensing community who are used to "pixel" processing * on the other hand, there are many situations in which the raster approach may appear to sacrifice too much detail o cartographers were appalled by the crude outlines of parcels that resulted in the "pinking shear" effect of diagonal boundaries represented by grid cell edges diagram o surveyors were dismayed by the "inaccuracy" caused by the cells when portraying linear features and points o situations in which the raster approach sacrificed too much detail * however, computing times for overlaying vector based information can be excessive o early polygon overlay routines were error-prone, expensive, slow * today, there are situations in which it is clear that one approach is more functional than the other o e.g. using "friction" layer to control width of buffer is only feasible in raster o e.g. viewshed algorithms to find area visible from a point are feasible with elevation grids (raster DEMs), not with digitized contours o e.g. land survey data can only be represented with precise lines * an important current trend involves linking raster and vector systems, displaying vector data overlying a raster base o raster data may be from a GIS file (perhaps a remotely sensed image) or from a plain scanned image file * therefore, the question has evolved from "Which is best?" to
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u21-THE RASTER VECTOR DATABASE DEBATE - UNIT 21 - THE...

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