Editing existing features

Editing with sketches

In addition to constructing new features, sketches can be used to modify existing features. For example, to reshape a polygon, you can construct a sketch of the new edge, or you can use a sketch to divide one polygon into two.

You can insert or delete vertices in a sketch to modify a feature''s shape. You can also trim and extend lines and split lines and polygons by drawing a sketch. When you use a sketch to modify an existing feature, you complete the update by finishing the sketch.



Adding attribute information
Attributes are descriptions of a geographic feature in a GIS, usually stored as a row in a table. For example, attributes of a river might include its name, length, and average depth. You can enter new attribute values when you create features, and you can edit existing values. When you create a new feature, it starts with only the default attribute values. You input attributes after you create a feature.

You add and modify the attributes of features within an edit session. You can edit attribute values manually by typing in new values or by copying and pasting existing values. Some features are designed with subtypes, default values, and attribute domains. These can make it easier to edit values and can help prevent data entry errors. After you modify attributes that have range domains, you can validate your edits to check that the new values fall within the valid range.

If there are relationships between feature classes and tables in your geodatabase, you can find the objects related to a particular object and edit them. For example, if you have a table of landowners that is related to a parcel feature class, you can select a parcel feature, use the relationship class to find the owner of that parcel, then edit some of the attributes in the owner table. Some relationship classes have rules that control how features can be related. After you edit related geodatabase features or tables that have relationship rules, you can validate your edits to check that the related objects still conform to the relationship rules. You can also establish a new relationship between objects or break existing relationships.

Learn more about editing with subtypes, default values, and attribute domains
Learn more about editing relationships and related objects
Learn more about creating relationship classes



Methods of editing attributes

There are two main ways of adding or updating attributes in ArcMap: the Attributes dialog box and the table window.

The Attributes dialog box displays attributes of selected features and shows you the raw data and fields as they are stored in your geodatabase. The left side of the dialog box shows the name of the layer to which the selected feature or features belong, while the right side shows the attribute values

You can also open a table window to see all the tabular information about a layer or table. The table window displays field aliases, which are often more user-friendly names for your fields, and can hide the fields you don''t want to see. To add or change a value in the table window, simply click a cell and type the new value. The table window also allows you to use the Field Calculator, which helps you update multiple values in a particular field and allows you to use advanced Visual Basic for Applications (VBA) statements when editing field values. Although you don''t have to be in an edit session to calculate field values, an edit session is recommended because it allows you to undo your edits.
Updating data using SQL

You can use Structured Query Language (SQL) outside ArcGIS to perform bulk attribute updates on your data. However, you need to have a good understanding of your data model when using this approach to ensure that the chance of data corruption is minimized and any attributes you update do not affect other objects in the database through relationships or other behavior.

Learn more about updating data with SQL




Creating new text features
You can store map text as annotation in a geodatabase. Annotation provides flexibility in the appearance and placement of your text because you can select individual pieces of text and edit them. Dimension features are a form of annotation designed to express distance measurements. Geodatabase annotation and dimension features are created and edited inside an edit session.

You can create and edit annotation with the specialized annotation editing tools. You''ll follow a similar process as with editing other features: choose the layer and the method you want to use to create the annotation and use the Sketch tool to create the feature.

Some annotation feature classes stand alone in the geodatabase. These are known as standard annotation. Standard annotation is not formally associated with features in the geodatabase. For example, you might have a piece of standard annotation that represents a mountain range, ocean, or administrative boundary; the annotation simply marks the general area on the map.

Another kind of annotation, known as feature-linked annotation, is associated with the feature it is describing through a relationship class. The text reflects the value of a field or fields from the feature to which it''s linked. You might use feature-linked annotation to identify features such as parcels, streets, rivers, roads, or cities. With feature-linked annotation, as you create new parcels or street features, for example, using the editing tools in ArcMap, annotation will be created automatically.

You can create dimension features with different methods and modify where they are placed and how they look. Dimension features are stored in dimension feature classes and can be placed and edited using the tools on the Dimensioning toolbar.
Enhancing productivity while editing
Many editing operations can be made more efficient and accurate using some of the functions in the editing environment.



The snapping environment

Snapping is one of the easiest ways to more accurately position new vertices and segments as well as features as you move them. Snapping can help establish exact locations in relation to other features. When snapping is turned on, your mouse pointer will jump, or snap to, edges and vertices when your pointer is near them. This means the pointer is within the snapping tolerance. Snapping can help you with many editing operations, for example, creating polygons that do not overlap or have gaps between them or placing a point exactly along an existing line.
Learn more about the snapping environment




Shortcut menus, keyboard shortcuts, and distance units abbreviations

The shortcut (context) menus for many tools, especially the Sketch tool, provide commands that help you place vertices and segments more easily and accurately. You open a shortcut menu by right-clicking the map with a particular tool.

Many editing functions have keyboard shortcuts associated with them including those on the shortcut menus. If you learn some of the most common shortcuts, you can minimize the use of your mouse and speed up your edits. For example, with the Sketch tool active, you can press the F6 key to quickly enter the coordinate location of the point or vertex you want to place. You can also switch to a different editing tool or quickly change to a navigation tool to zoom or pan the map by pressing different keys.

Sometimes you may need to enter lengths or other measurements in units different from your map units. In many dialog boxes throughout the editing environment that require you to enter a distance value, you can specify values in different units of measure by simply typing a unit abbreviation after the number. For example, if your map units are feet, by default, ArcMap will assume any distance values you enter are in feet. However, you can simply add "m" after your input value so ArcMap knows the value you entered is actually in meters.

Caching data for better performance

When you are editing data in a geodatabase, especially an ArcSDE geodatabase, you may want to turn on the map cache, which allows temporary storage of geodatabase features from a given map extent in the desktop computer''s memory. Building a map cache can reduce the load on your network and the geodatabase since ArcMap accesses this information from your computer''s RAM, reducing the number of queries the client needs to execute on the server.

Learn more about the map cache


Opening additional windows

You can also use additional windows in ArcMap�magnifier, overview, and viewer windows�to get different views of your data, which can help when editing. You can get a closer view of a small area without changing the map extent (magnifier window), see the full extent of your map (overview window), or get an independent view onto the map (viewer window). For example, a magnifier window can be turned on before or during the creation of new features and modification of existing features. You can click the heading of the magnifier window and drag it while holding on to the same sketch or modification already in progress. Viewer windows can be used on computers with dual monitors, so you can open and maximize the viewer window on the second monitor to provide a large-scale view of the area currently being edited. Editing can be performed in both displays, and graphic feedback shown while you edit appears simultaneously on both displays.

Learn more about magnifier, viewer, and overview windows




Integrating data
GIS data often comes from many sources. Inconsistencies between data sources sometimes require you to perform additional work to integrate a new dataset with the rest of your data. Some data is geometrically distorted or rotated with respect to your base data. You may also need to edit boundaries that are shared by multiple features or implement additional methods of maintaining the integrity of your data.




Performing spatial adjustments
Within the editing environment, the spatial adjustment tools provide interactive methods to align and integrate your data. Spatial adjustment supports a variety of adjustment methods and will adjust all editable data sources. It''s often used when you''ve imported data from another source, such as a CAD drawing or a 3D multipatch model. Some of the tasks you can perform include converting data from one coordinate system to another, correcting geometric distortions, aligning features along the edge of one layer to features of an adjoining layer, and copying attributes between layers. Since spatial adjustment operates within an edit session, you can use existing editing functionality, such as snapping, to enhance your adjustments.

In addition, using a magnifier window when you''re performing spatial adjustment allows you to get a better view of the origin and destination locations so you can place links more accurately without changing the extent of the map. You can open a magnifier window above the start point of the link, add the link, then move the window to the destination location and add that link without having to zoom and pan the map.

Editing shared geometry
You may find that you need to edit the geometry of multiple features at once. Using the topological association among features, you can move boundaries and vertices shared by multiple features. For example, you can move a border to update two forest polygons or, as seen in the graphic below, move a corner vertex and update several parcel polygons and a few lot boundaries at the same time.

Within the editing environment, you can create a map topology that enables you to edit the shared parts of features. A map topology is a temporary set of topological relationships between coincident parts of simple features on a map. The primary types of geometry that are acted on when editing a map topology are edges, which are line segments that define lines or polygons, and nodes�points at the end of an edge. When you move a node in a topology, all the edges that connect to it are stretched to stay connected to the node. When you move an edge, edge segments stretch to maintain the connection of shared endpoint nodes to their previous location. You can also move a node and a connected edge without stretching the other connected edge by temporarily splitting the topological relationship between the node and the other shared edges.

When creating a map topology, you need to specify which layers will participate in the topology and the cluster tolerance to use to determine which parts of the features are coincident and which edges and nodes in the topology are shared.




Maintaining spatial integrity
Beyond editing shared geometry, topology within a geodatabase allows you to maintain additional spatial integrity by specifying a set of rules to apply to your data, allowing you to find and fix any errors and validate the relationships.



Topology

Topology is a collection of rules that, coupled with a set of editing tools and techniques, enables the geodatabase to more accurately model geometric relationships. ArcGIS implements topology through a set of rules that define how features may share a geographic space and a set of editing tools that work with features that share geometry in an integrated fashion. A topology is stored in a geodatabase as one or more relationships that define how the features in one or more feature classes share geometry. The features participating in a topology are still simple feature classes�rather than modifying the definition of the feature class, a topology serves as a description of how the features can be spatially related.

For example, in the graphic below, the coral-colored squares and lines indicate errors in topology, which is one way of ensuring spatial integrity. These may be locations where there is a line that does not connect to another line (known as a dangle), a polygon that does not contain a point within its boundary, or some other violation of a rule imposed on the geodatabase.
ArcGIS provides a set of editing tools that help find and fix topology rule violations. Violations of topology rules are initially marked as errors in the topology, but where appropriate, you can mark them as exceptions. Within the editing environment, you can use the tools on the Topology toolbar to locate errors, fix errors interactively or automatically, validate edits, and create new features from the geometry of existing features. Dirty areas track the places where topology rules may have been violated during editing. Depending on your workflow, you can validate topology rules and clean up dirty areas after each edit session or on a schedule.