WIRKING WITH FEATURE DATA

WIRKING WITH FEATURE DATA: COVERAGES AND SHAPEFILE (see editing http://educationally.narod.ru/gisgraph5photoalbum.html)
Field-based feature model and database management system both coverage and shapefile. These models use a georelational data model , by storing vector data for the features in binary files and using unique identifiers to link features to attributes. The attribute are stored in feature attribute tables in other files.

COVERAGES are the traditional format in ArcInfo for complex geoprocessing, building geographic datasets and special analysis. Coverages contain primary(labeled as points, line, and polygons) composite (routes/section and regions), and secondary (tics, links and annotations) feature types.

SHAPEFILES are stored in folder and consist of a set of files of vector data in the shapefile and a dBASE (*.dbf) file containing the attribute of the features. Each constituent file shares the shapefile name. The shapefile usually consists of 3-5 separate files *.dbf (it reads by Excel, Access and etd), *.shp, *.shx, *.shn, and *.sbx.

Shapefiles can be created by other shapefiles. This option allows you to do same manipulation of data without modifying the original shapefile. DRAW TOOLS allows you do it. The shapefiles can be deleted, edited vertex by vertex, copied, pasted, unioned, or split (ARC/INFO type operations).

If you are copying a shapefile to another directory, you must make sure to include all the files associated to that shapefile, otherwise ArcMap will not recognize the file. To COPY a shapefile, right-click on the name and select copy from the context menu. The new shapefile can be pasted into existing or new Map View.

CREATING SHAPEFILES FROM SELECTED DATA
- Right-click on the SELECTION SET and choose “Create a layer from selected features”
- Name the new layer
- Clear all the selected features from the original layer

CREATING SHAPEFILES BY “DRAWING” OR DIGITIZING ON SCREEN

To create a new feature, you create an edit sketch. A sketch is a shape drawn by digitizing vertices. The sketch can be used to complete various tasks; these tasks are listed in the TASK dropdown list available from Editor Toolbar.

EDITING OPTIONS:
-Merge – combines two or more map features into one feature
-Union – unions polygons
-Intersect – common area
Split – splits and applied to single feature
-Cut, copy, delete, paste – features copied and pasted within and between themes
-Clip – removes features and portions of features which lie outside of the features of another layer

SETTING EDITING PROPERTIES FOR SHAPEFILES

Snapping rules – allows snapping to existing features but only in the theme being edited, not to features in other themes. Ensures that features within a specified distance are automatically adjusted to meet at exactly the same location.

Attribute updating rules – how attribute properties are handled for each data field when features are Unioned or Split
-Add/Subtract – for unioned/split features the values will be added/subtracted
-copy – copies the value of the feature that is first in the table. By selecting and then using “PROMOTE TO TOP” button, you can control the order of features in the table when copying values.
-Average – averages the value of combined or unioned features.
-Proportion – values for edited features will be proportional area or length.

CREATING AND EDITING SHAPEFILES
Make shapefile/layer active and open the Layer Properties, select FIELDS. The Shape fields is visible. Turn Shape fields on. Create your selection SELECT BY ATTRIBUTES. Apply. Right-click on layer and do Data-Export Data from the context menu. Save the shapefile in your folder and add it to a Map View – export data as a new layer.
Clear selection Attribute table-Options-Clear Selection
Create a new data frame (from Insert) and name it.
Select Editor-Start Editing –Sketch tool, and create new Feature from the dropdown menu. With this tool draw the polygon you need. When finished, double-click and ArcMap adds the final segment of the sketch and the sketch turns into a feature.

In the MAP VIEW (arcMap, arcView), toggle the Selection button at the bottom of the Table of Contents. The polygon sketch will be listed as selection. “Create a new layer from selection”. Name it. To convert it into a shapefile, right-click to bring the context menu and select Data-Export Data (same coordinate system), say YESto add the new shapefile to the document. Right-click on the new file to bring up the Context Menu, select the Symbology tab and select “hollow” with an outline of 2(3,4…)

Maintaining attribute integrity
ArcGIS provides tools to help you maintain the quality of your attribute data, primarily through the use of attribute domains.



Using attribute domains

Attribute domains are rules that describe the permissible values of a field type and are used to constrain the values allowed in any particular attribute for a table, feature class, or subtype. Each feature class or table can have a set of attribute domains that apply to different attributes. A given attribute domain can be shared by various feature classes and tables in a geodatabase. If a feature class has subtypes, each subtype can have a different domain associated with a given attribute. For example, a water mains feature class and a water laterals feature class can use the same domain for their ground surface type fields.

When you edit a field with a coded value domain, a drop-down list of all the domain values appears. When you choose one of the values from this list, you know that you are assigning the field a valid value.
A range domain specifies a valid range of values for a numeric attribute. For example, you could have three subtypes of water mains: transmission, distribution, and bypass. Each of these could have a different range of valid pressures. Distribution water mains can have a pressure between 50 and 75 psi. For a distribution water main object to be valid, its pressure value must be between 50 and 75 psi. A range domain specifies this range of values.


Result on attribute domains after splitting and merging features

Often when editing data, a single feature is split into two features or two separate features are combined, or merged, into a single feature. For example, in a land base database, a land parcel may be split into two separate land parcels due to rezoning. Similar zoning changes may require two adjacent parcels to be merged into a single parcel.

The behavior of an attribute''s values when a feature is split is controlled by its split policy, and when two features are merged, an attribute''s value is controlled by its merge policy. Each attribute domain has both a split policy and a merge policy. When a feature is split or merged, ArcGIS looks to these policies to determine what values the resulting feature or features will have for a particular attribute.

Creating and Editing Feature Data
An overview of editing and data compilation
Tutorial --
Sketch tool