Lecture 7 Digitizing Dr. Zhang Spring, 2017
Model of the course Using and making maps Navigating GIS maps Map design Working with spatial data Geoprocessing Spatial data infrastructure Digitizing File geodatabases Geocoding Interactive maps Map Animations Map layouts Spatial analysis 3D GIS Proximity analysis Raster analysis Analyzing Spatial data Network analysis Data mining Spatial regression
Outline Digitizing overview GIS features Digitizing features in ArcMap Advanced digitizing tools Transforms and spatial adjustments 3
Lecture 7 DIGITIZING OVERVIEW 4
Why digitize? New maps Map features are wrong Missing features Other? 5
Heads down digitizing Digitizing tablets Used to digitize hard copy maps into GIS Transform wire intersections into coordinates of the tablet s coordinate system
Steps for heads down digitizing Tape map to the digitizing tablet Register control points on the map Control points Puck Estimate two conversion equations (one for vertical and one for horizontal coordinates) Tape Digitize vectors (points, lines, or polygons) Map 7
Heads up digitizing Mouse on a screen Digitizes paper maps, aerial photos, or other images 8
Lecture 7 GIS FEATURES 9
Points Single features Nodes Line endpoints Vertex points Controls shapes of lines and polygons 10
Creating points Heads up digitizing Single point features Sketch tool and snapping features Points added as XY event files (chapter 4) Points added using geocoding functions (chapter 8) 11
Lines Starting and ending points with shape vertex points as needed Vertex points 12
Line attributes Shape From and To attributes Node Address (street centerlines) Lat/long Length 13
Polygons Three or more lines joined to form a closed area Single polygons or multipart features Hawaiian islands can be multiple polygons as one feature 14
Polygon attributes Shape Area Perimeter Length 15
Constructions tools Points Lines Polygons 16
Lecture 7 DIGITIZING FEATURES IN ARCMAP 17
Create new feature class In Catalog Navigate to desired location Create new feature class or shapefile Add spatial reference information Add new fields (optional) 18
Digitize new features In ArcMap Create base map Add feature class Start editing Digitize feature Stop editing and save 19
Create base map Vector features or raster images Add features 20
Start editing Start editing 21
Begin digitizing pick points 22
Stop editing Editor toolbar, Stop editing Save edits 23
Edit attribute data Start editing, populate fields in table (create fields if necessary) 24
Lecture 7 ADVANCED DIGITIZING TOOLS 25
Specify angle and length Lines and polygons Straight segment tool Type length and angle 26
Snapping tools Snapping toolbar 27
Trace tool Good for complicated shapes Editor toolbar,trace tool 28
Generalize tool Creates features for use at small scales with less detail while preserving basic shapes US Census cartographic boundary files Census TIGER water features Generalized/Small scale Modified rivers Smoothed/Large scale 29
Smooth tool Smoothes sharp angles in polygon outlines to improve aesthetic or cartographic quality Smooth before Smooth after 30
Cut polygons Creates two polygons from one original Cut polygon tool Polygon before Polygon after 31
Move and rotate Adjusts features Polygon before Polygon after 32
Lecture 7 TRANSFORMS AND SPATIAL ADJUSTMENTS 33
Transforms Converts data From one coordinate system to another. From digitizer or scanner units to real world coordinates. Shifts data Within a coordinate system, (for example, feet to meters). 34
Rubbersheeting Geometric distortions commonly occur in source maps May be introduced by imperfect registration in map compilation Lack of geodetic control in source data Variety of other causes Corrects flaws through the geometric adjustment of coordinates 35
Edgematching Aligns features along the edge of one layer to features of an adjoining layer Layer with the less accurate features is adjusted, while the adjoining layer is used as the control. Attribute transfer is typically used to copy attributes from a less accurate layer to a more accurate one. 36
Spatial adjustment example CAD drawings (buildings) Generally do not have geographic coordinates Hamburg Hall CAD drawing Hamburg Hall Ortho photo 37
Spatial adjustment example Spatially match drawing to map using displacement links 38
Summary Digitizing overview GIS features Digitizing features in ArcMap Advanced digitizing tools Transforms and spatial adjustments 39
Lab Tutorial 7-1 (p256) Tutorial 7-5 (p279) 40