Vector-Based GIS Data Processing. Chapter 6

Vector-Based GIS Data Processing Chapter 6

Vector Data Model Feature Classes points lines polygons Layers limited to one class of data Figure p. 186

Vector Data Model Shapefiles ArcView non-topological most methods discussed in book will work in ArcView (the program compensates)

Characteristics of Vector Processing compares layers features within layers layers with features in other layers features with features in other layers attributes topological relationships connectivity adjacency containment note: must maintain topology when altering data

Data record ground coordinates in double-precision accuracy varies with data collection methods errors may propagate

Data Processing Functions Figure p. 188 (top) input analysis: figure p. 188 (bottom) output

Vector Data Input: Phases acquisition digitizing maps or remote-sensing data table top or scan & vectorize import existing data field collection editing formatting/translating linking

Digitizing Existing Maps Digitizers parts: table, cursor, controller specifications table size resolution accuracy: stability, repeatability, skew process figure p. 190

Digitizing Existing Maps preparation check source quality obtain control points (tic points) prepare specifications: fig p. 191 (top)

Digitizing Existing Maps digitize template fig p. 191 (bottom) features common to all layer neat lines tic points common elements create only once save time ensure accurate overlay source base map input coordinates edit & build topology

Digitizing Existing Maps Digitize map register map one layer at a time digitize all lines (spaghetti model) stream mode vs point mode mark lines as digitized only lines appropriate for layer post-digitizing data processing assign IDs editing: map must remain on digitizer until this step is complete

Scanning & Vectorization heads-up digitizing scanning: raster (or other) image raster-vector conversion processing

Scanning scanner specifications resolution accuracy scan size output format software quality process quick input no layers (entire map is scanned)

Raster-Vector Conversion automatic must be started must be watched problems: broken lines, thin lines, contrast manual ( heads-up ) time-consuming least editing (potentially)

Raster-Vector Conversion text - automatic symbol - manual graphical editing

Importing Vector Data outside source metadata translator field survey (imports points) direct via table CAD

Importing Vector Data transformation ground coordinates projection need metadata need to understand what was used (and will be used) and why

Graphical Data Editing errors (fig p. 195) intersection errors node errors polygons are closed polygon labeling topology process set environment build topology edit & correct join adjacent layers

Graphical Data Editing set editing environment fig p. 196 edit tolerance weed tolerance grain tolerance

Graphical Data Editing topology building build structure & relationships fig p. 197 identify errors & automatically correct fuzzy & dangling tolerance [fig p. 198 (top)] rebuild topology (& repeat) data editing & error correction fig p. 198 (bottom) back up file before & during editing

Graphical Data Editing join adjacent layers (if necessary) fig p. 199 edge match join maps dissolve redundant polygon boundaries rebuild topology

Attribute Data Conversion vector data, no attributes steps to creating attribute table(s) define structure of data file populate data file manual entry add ID column to existing data table check for errors link to associated layers

Attribute Data Conversion event themes (ArcView) XY uses XY coordinates in a table creates a point theme point, linear, continuous, address uses existing shape file as reference creates point or line theme

Vector-Based Data Analysis attribute database query analysis of attribute table data selected items - fig p. 202 retrieve associated graphical elements may build new table operations - fig p. 203 select project join ArcView: Query Builder

Vector-Based Data Analysis statistical computation mean, max, min, std. dev., quantile ArcView display within a theme can summarize attributes of one theme based on polygons in another theme

Vector-Based Data Analysis address geocoding - fig p. 204 provides street addresses with XY coordinates uses reference theme projected line file of street network with address ranges U.S. Census TIGER files event table contains street addresses geocoding editor both input files must be compatible with editor parses event table addresses compares addresses to reference data creates new point file and table with XY coordinates

Vector-Based Data Analysis calculation of areas, perimeters & distances feature-based overlay analysis point-in-polygon - fig p. 207 (upper left) drops line downward from point buffering (feature-based) - fig p. 207 (upper right) point, line, polygon edge (inside or outside) buffer zone is a polygon - fig p. 208 neighborhood analysis fixed or variable distance - fig p. 208

Vector-Based Data Analysis reclassification (layer-based) fig p. 209 simplification select attribute data assign new, common value merge appropriate adjacent polygons

Vector-Based Data Analysis layer-based overlay analysis features of two layers are intersected point on polygon line on polygon polygon on polygon creates new layer and attribute table - fig p. 210

Vector-Based Data Analysis layer-based overlay analysis (con t) operators - fig p. 211 union intersect identity clip (cookie cutter) erase cov split

Vector-Based Data Analysis layer-based overlay analysis (con t) define objectives & data analysis criteria apply topological overlay operators - fig p. 212 & 213 postoverlay processing & interpretation of results removal of sliver polygons - fig p. 213 use template use tolerance or sliver criteria

Vector-Based Data Analysis network analysis interconnected, linear features network layer - fig p. 214 line segment/edge (has many attributes) junction/intersection (point or node) turn (attribute of junction)

Vector-Based Data Analysis network analysis (con t) functions pathfinding - fig p. 215 allocation tracing spatial interaction (uses gravity modeling) distance matrix location-allocation modeling

Vector-Based Output Functions presentation methods - fig p. 217 map composition - Chapter 7 vector-raster conversion lose attributes

Vector Application Programming tool-box approach extensions scripts advantages standardize processes automate frequent functions enhance capabilities

Vector Application Programming internet map server fig p. 223