Transcript

GIS Tutorial 1

Lecture 6Digitizing

Outline

Digitizing overview

GIS features

Digitizing features

Advanced digitizing tools

Spatial adjustments

Digitizing sources

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DIGITIZING OVERVIEWLecture 6

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Why digitize?

New maps

Map features are wrong

Missing features

Other?

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Digitizing tablets Used to digitize

hard copy maps into GIS

Transform wire intersections into coordinates of the tablet’s coordinate system

Heads down digitizing

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Steps for heads down digitizing Tape map to the

digitizer Register control

points on the map Estimate two

conversion equations (one for vertical and one for horizontal coordinates)

Digitize vectors (points, lines, or polygons)

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Control points

Map

Puck

Tape

Heads up digitizing Mouse on a screen Digitizes paper maps, aerial photos, or

other images

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GIS FEATURESLecture 6

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Points

Single features

Nodes Line endpoints

Vertex points Controls shapes of lines

and polygons

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Creating points

Heads up digitizing Single point features Sketch tool and snapping features

Points added as XY event files Points geocoded using addresses

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Lines Starting and ending points with shape

vertices as needed

Vertex points

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Lines Physical attributes of TIGER streets

Shape From and To attributes

Node Address Lat/long

Length

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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)

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Polygons

Physical attributes Shape Area Perimeter Length

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DIGITIZING FEATURESLecture 6

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Create new feature class Created in ArcCatalog

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Create new feature class

Add spatial reference information

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Create new feature class

Add new fields

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Create new feature class

Feature class created

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Creating Feature Layers or Shapefiles in ArcMap

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Within ArcMap:

-Locate an existing data layer that is similar to the layer that you wish to create.

-Start editing the existing layer, then digitize the new feature

-Select the new feature

-Export the selection to a shapefile

-Add the shapefile- fields already present and map projection is already defined -Examples in the instructor exercise

Digitize new features Create base map Add feature in ArcMap Start editing (Editor toolbar) Digitize feature Stop editing and save

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Create base map for digitizing Vector features or raster images

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Add new feature class

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Add Editor toolbar Customize, Toolbars, Editor toolbar

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Start editing Editor, Start editing

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Begin digitizing

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Click point (tree) locations

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Stop editing Editor, Stop editing

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Edit attribute data Start editing, populate fields in table

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ADVANCED DIGITIZING TOOLSLecture 6

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Specify angle and length

Lines and polygons

Straight segment tool

Type length and angle

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Snapping tools

Snapping toolbar

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Point Snapping

Endpoint Snapping

Vertex Snapping

Edge Snapping

Trace tool Good for complicated shapes Editor toolbar, Trace tool

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Generalize tool Creates features for use at small scales

with less detail while preserving basic shapes

U.S. Census cartographic boundary files

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Census TIGER water feature City planning rivers

Smooth tool Smoothes sharp angles in polygon

outlines to improve aesthetic or cartographic quality

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Smooth before Smooth after

Cut polygons Creates two polygons from one original Cut polygon tool

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Polygon before Polygon after

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SPATIAL ADJUSTMENTSLecture 6

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Transforms Converts data

from one coordinate system to another. from digitizer or scanner units to real world

coordinates.

Shifts data within a coordinate system, (e.g. feet to meters).

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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

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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.

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Spatial adjustment example Hamburg Hall CAD Drawing

CAD drawings generally do not have geographic coordinates

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Spatial adjustment example Spatially match drawing to map using

displacement links

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DIGITIZING SOURCESLecture 6

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USGS

United States Geological Survey

Common Data Types & Standards Digital Elevation Models (DEMs) Digital Orthophoto Quads(DOQQs) Digital Line Graphs(DLGs) Digital Raster Graphics (DRGs) Landsat Satellite Images Land Use Land Cover (LULC) Spatial Data Transfer Standard(SDTS)

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Orthophotography Digital imagery in which distortion from

the camera angle and topography have been removed, thus equalizing the distances represented on the image

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Digital Ortho Quarter Quads—DOQQs

http://online.wr.usgs.gov/ngpo/doq/ Grayscale or color-infrared (CIR) images 1-meter ground resolution; Cover an area measuring 3.75 minutes

longitude by 3.75 minutes latitude, approximately 5 miles on each side

Referenced to the North American Datum of 1983 (NAD83) and cast on the Universal Transverse Mercator (UTM) projection

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DOQQ image resolutions The ground length of one pixel of the

image image with one meter resolution means

that each pixel in the image represents one square meter on the ground.

30 meters30 meters 10 meters10 meters 5 meters5 meters

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DOQQ image resolutions

2 meters2 meters 1 meter1 meter

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National Elevation Data Sets United States Geological Survey

(USGS) National Elevation Dataset (NED) Shaded Relief Imagery Data (Free)

Maps provide highest-resolution elevation data available across the United States, in raster format

http://ned.usgs.gov/

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Scanning paper documents Raster to vector conversion Paper (historic) maps Scanned maps and images become

vectors Special software needed

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Summary

Digitizing overview

GIS features

Digitizing features

Advanced digitizing tools

Spatial adjustments

Digitizing sources

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