esrm 250/cfr 520 autumn 2009 phil hurvitz

ESRM 250 & CFR 520: Introduction to GIS

© Phil Hurvitz, 1999-2009

ESRM 250/CFR 520Autumn 2009Phil Hurvitz

Creating Feature Datasets

(vector data)

2



DigitizingCreating vector data

setsConverting to feature

classCreating new

datasetsSnappingAltering the shape of

lines and polygonsSplitting features

Unioning polygonsMerging polygonsIntersecting polygonsClipping polygonsAdding attributesUndoing editsSaving edits

Overview



most common “legacy” method of getting data into a GIS

Digitizing

tedious & detail-oriented work



How the digitizing tablet works

Digitizing tablet

operatorclicks on or traces features

y = 10

x = 5

coordinates are placed in database



ArcGIS supports creation & editing of vector data sets (shapefile & geodatabase = “feature class”)

Point Line Polygon

Data sets are completely editable Coordinate data Attribute data

Creating vector data sets



Any supported vector data set can be converted to feature class

Converting to feature class

CAD data



Any supported vector data set can be converted to feature class


shapefile or gdb feature class



Selected sets are converted




New datasets can be created from scratch in ArcCatalog

decide in advance what feature type to represent the data

Creating new datasets

select feature type



New datasets can be created from scratch in ArcCatalog

specify coordinate system




Creating new datasets: “heads-up” digitizing

Done completely on computer (no digitizing tablet), hence the term “heads-up”



Create a road layer using a photo background




New features can be created from tracing existing selected features




Snapping controls: how features align during creation/editing connections of lines (node placement) completion of polygons avoid overshoots/undershoots avoid slivers or gaps

Snapping



Snapping behavior controlled by the Snapping Environment dialog

Snapping



Snapping



Interactive snapping options Snap to an existing vertex Snap to an existing line segment or

polygon edge Snap to an intersection of two or more

lines Snap to an existing line endpoint Snapping can be layer-to-layer

Snapping options



Snapping

Helps avoid these errors

J. Lawler



Topological editing: shared edges are all affected by edits

Altering the shape of lines and polygons



Non-topological editing: only a single feature is edited

Altering the shape of lines and polygons



Polygons are split by a user-defined line

Splitting (cutting) polygons



Lines are split at a specified location

Splitting lines



Geodatabase splitting policiesAttributes are handled by policies Duplicate: values in new records are

copied from the parent record Geometry property (e.g., area, perimeter,

length) automatically handled Geometry ratio

based on geometry (e.g., percent of area)

Splitting features



Attribute splitting (for geodatabase feature classes) is handled by policies

Splitting features

image from ESRI



Merging polygons

select multiple polygons from the same layer

original polygons are merged into a single new polygon



Attributes are handled by rules in the same way as splitting

Merging polygons

image from ESRI



Merging polygons: an example

Merging polygons

J. Lawler



Similar to merge, but can combine features from > 1 layer

Unioning polygons



Intersecting polygons

spatial area as the "set" for intersection

a new polygon from common areas

like mathematical intersection



Clipping polygons

Option 1: discard the intersection



Clipping polygons

Option 2: keep only the intersection



Clipping: an example

J. Lawler



Landscape metrics calculated from clipped frog home range

% forest 73% ag 12Ag dist

20F-patch.s 60A-patch.s 6

Clipping: an example

J. Lawler



Attributes need to be defined for new datasets

Fields are added; define field name data type width decimal precision

Adding attributes



Adding & defining fields: note field names & data types

Adding attributes



After fields are added, attributes can be updated

Adding attributes



Edits can be undone in reverse order

Edits can be undone up to the previous save (or creation)

Once a dataset’s changes are saved, edits cannot be undone

It can be good to have a backup of the data created before an editing session

Undoing edits



Save EARLY and OFTEN

You are prompted to save edits when: Dataset is closed for editing Another dataset is opened for editing Document is saved or closed ArcGIS is closed

Saving edits

esrm 250/cfr 520 autumn 2009 phil hurvitz

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