Transcript Vector-Based GIS Data Processing Chapter 6 Vector Data Model Feature Classes points lines polygons Layers limited to one class of data Figure p.

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
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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
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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
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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