Event Theme

A theme is a set of geographic features in a view. A theme represents a source of geographic data such as:

• A spatial data source such as an ARC/INFO coverage or ArcView shapefile.
• A CAD drawing such as an AutoCAD drawing (if ArcView’s CAD Reader extension is loaded)
• An image data source such as a satellite photo.
• A table containing XY coordinates, street addresses that can be geocoded in ArcView, or events that can be matched to route features.
• A data layer managed by by ESRI’s Spatial Database Engine (SDE) (if ArcView's Database Themes extension is loaded).

If you have a table containing data about the features displayed on a view... For example, a dBASE file of business data on a state-by-state basis that you want to visualize on a view containing the states.

You can join this table to the existing table for these features. This allows you to symbolize, label, classify, query and analyze these features according to their values for the fields in your table.  If you have a table containing XY coordinates...
For example, a table containing the results of an SQL query that retrieved information about test drilling sites in a particular oil field including their latitude-longitude locations, or a table containing latitude longitude locations taken from a GPS receiver..

You can add this data to a view as a theme. Each record in the table will be displayed on the view as a point feature. You can then work with this theme like any other theme.

Working with event tables in ArcView

Events enable you to map data that contains geographic locations but which is not in a spatial data format. For example, you might have a file of customers and want to make a map showing how they are distributed throughout the region. Or you may have a table of accident information and want to display the accidents with reference to their milepost locations along a route. Or you might have a table with information about bird sightings, with the latitude-longitude location of each sighting as fields in the table. In ArcView these are all examples of events.

Here are the types of events that ArcView supports:

XY event tables
These tables contain the exact position of features as XY coordinates, such as the location of fire hydrants in a city or the points where soil samples have been taken. XY coordinates can be obtained by reading a map, measuring positions on a view, field surveying, using a GPS (Global Positioning System) receiver, geocoding the table that contains address information, etc. The XY coordinates can be in any coordinate system and units, such as longitude-latitude, or meters.

Point event tables
These tables contain the locations of points specified as positions on a route system in an ARC/INFO coverage. For example, a point event table might record the location of bus stops along a bus route defined by their distance from the start of the route, rather than their XY coordinate location. "At 12.5 miles along Route 10" is an example of a point event.

Linear event tables
These tables define the from and to position of events along a route system in a coverage. For example, a line event table might record the pavement quality along different sections of a highway, where the sections are defined by distance along the highway.

Continuous event tables
These tables define linear events that record only the point where a change occurs. This is a useful method for recording data which has no gaps, such as the location of speed zone changes along a highway, with the location defined by distance along the highway.

Address event tables
Address event tables contain the street addresses or certain kind of locational identifiers of anything: customers, suppliers, competitors, branch offices, facilities, crimes, etc. See Tables that can be geocoded and Address components for information about the formats of address you can use for geocoding.

Add Event Theme (Dialog box)

Adds a new theme to a view using a table containing events in your project as the data source.

Dialog box options

XY - each record in your table represents a point feature located at a X, Y coordinate point. XY events are added to the active view as a theme based on the map extent and map unit specified for the view in the View Properties dialog.

Routes - each record in your table represents a point feature located at a position on a route system in an ARC/INFO coverage. Route events are added to a view based on whether the active theme contains a route system. The route category button is disabled if the active theme does not contain a route system. To make the route category button available, add a route theme and make it active.
When you select any of these categories the panel on the dialog box will change to reflect appropriate fields for the type of event chosen.

Adding XY Events

Table The drop-down list shows all the tables in your project. Select the table that contains XY events. When you select a table, ArcView reads the field names in the table to find likely defaults for the options below it.
X field The field in the table that contains the X-coordinate or longitude data.
Y field The field in the table that contains the Y-coordinate or latitude data.
Press OK to add the event source to the view.

Note If you want to select a field in the table but you can't see the field in the drop-down list, it is possible that the field has been hidden or renamed with an alias. In either case, you can open the Table Properties dialog to reveal the field and make it visible.