GIS Tutorial 1 Lecture 6 Digitizing. Outline Digitizing overview GIS features Digitizing features Advanced digitizing tools Spatial adjustments.

GIS Tutorial 1

Lecture 6Digitizing

Outline

Digitizing overview

GIS features

Digitizing features

Advanced digitizing tools

Spatial adjustments

Digitizing sources

2GIS TUTORIAL 1 - Basic Workbook

DIGITIZING OVERVIEWLecture 6


Why digitize?

New maps

Map features are wrong

Missing features

Other?


Digitizing tablets Used to digitize

hard copy maps into GIS

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

Heads down digitizing


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)

6GIS TUTORIAL 1 - Basic Workbook 6

Control points

Map

Puck

Tape

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

other images

GIS TUTORIAL 1 - Basic Workbook 77

GIS FEATURESLecture 6


Points

Single features

Nodes Line endpoints

Vertex points Controls shapes of lines

and polygons


Creating points

Heads up digitizing Single point features Sketch tool and snapping features

Points added as XY event files Points geocoded using addresses


Lines Starting and ending points with shape

vertices as needed

Vertex points


Lines Physical attributes of TIGER streets

Shape From and To attributes

Node Address Lat/long

Length


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)


0

0

1 2

43

Polygons

Physical attributes Shape Area Perimeter Length


DIGITIZING FEATURESLecture 6


Create new feature class Created in ArcCatalog


Create new feature class

Add spatial reference information



Add new fields



Feature class created


Creating Feature Layers or Shapefiles in ArcMap


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


Create base map for digitizing Vector features or raster images


Add new feature class


Add Editor toolbar Customize, Toolbars, Editor toolbar


Start editing Editor, Start editing


Begin digitizing


Click point (tree) locations


Stop editing Editor, Stop editing


Edit attribute data Start editing, populate fields in table


1 2

ADVANCED DIGITIZING TOOLSLecture 6


Specify angle and length

Lines and polygons

Straight segment tool

Type length and angle


Snapping tools

Snapping toolbar


Point Snapping

Endpoint Snapping

Vertex Snapping

Edge Snapping

Trace tool Good for complicated shapes Editor toolbar, Trace tool


Generalize tool Creates features for use at small scales

with less detail while preserving basic shapes

U.S. Census cartographic boundary files


Census TIGER water feature City planning rivers

Smooth tool Smoothes sharp angles in polygon

outlines to improve aesthetic or cartographic quality


Smooth before Smooth after

Cut polygons Creates two polygons from one original Cut polygon tool

GIS TUTORIAL 1 - Basic Workbook

Polygon before Polygon after

36

SPATIAL ADJUSTMENTSLecture 6


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).


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


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.


Spatial adjustment example Hamburg Hall CAD Drawing

CAD drawings generally do not have geographic coordinates


Spatial adjustment example Spatially match drawing to map using

displacement links


DIGITIZING SOURCESLecture 6


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)


Orthophotography Digital imagery in which distortion from

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


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


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


DOQQ image resolutions

2 meters2 meters 1 meter1 meter


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/


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

vectors Special software needed


Summary

Digitizing overview

GIS features

Digitizing features

Advanced digitizing tools

Spatial adjustments

Digitizing sources


GIS Tutorial 1 Lecture 6 Digitizing. Outline Digitizing overview GIS features Digitizing features Advanced digitizing tools Spatial adjustments.

Documents

basic workbook slide

digitizing slide

images gis tutorial

new fields gis tutorial

gis features lecture

features points

new features

digitizing features