Redding Holiday Inn and Convention Center
Wednesday, October 21, 1998
Room 1
10:15 a.m.--11:45 a.m.

The second ArcView session will present material for the more experienced user. The session will focus on using ODBC connectivity, creating and editing spatial data, and customizing ArcView to simplify routine tasks.

There is a lot of material to cover in the space of 90 minutes, and so the following background material has been prepared to give participants some additional information.

Open DataBase Connectivity allows users to bring tabular information from a separate database, such as MS Access, into an ArcView project. The data can be queried, joined, or linked to existing themes, but may not be edited without using advanced programming techniques. The basic functionality of ArcView's ODBC interface with MS Access will be demonstrated.

Before creating spatial data, check to see if what you need is already in digital form. Creating your own data is both time consuming and expensive. With the ever increasing amount of spatial data available, it may be prudent to use pre-existing data whenever possible, provided it meets the criteria of scale and detail you require. Many companies and organizations provide spatial data which can be used directly in ArcView. Unfortunately, in the case of agriculture, little spatial data exists, so CACs will need to consider building their own data layers.

Which Units Will a New Theme be Created In?: Before creating a new theme you should consider the theme's map units, as this will effect your ability to use the newly created theme with other spatial data. The units will vary depending on the map projection being used when the new theme is created. A geographic pojection (which uses a spherical coordinate system and so is, by definition, actually unprojected) uses coordinates of latitute and loingitude, which in ArcView are expressed as a decimal rather than in degrees, minutes and seconds. The State Plane coordinate system uses units of feet, the Albers Equal Area Projection system used by DPR uses units of meters, as does the UTM projection.

1. If you create a theme in a view that contains no other themes, and no projection has been specified for the view, the shapefile that is created is stored in whatever map units have been specified for that view. To review or specify the view's map units, choose Properties from the View menu.

2. If you create a new theme in a view for which a projection has been specified, the shapefile will be stored in units of decimal degrees. To review or specify the view's projection, choose Properties from the View menu, and click on the Projection button. The spatial data you create will align correctly with any themes based on data sources that are also stored in decimal degrees.

3. If you create a theme in a view that contains themes based on data sources that are not in decimal degrees (i.e. this data is stored in the same projected units such as State Plane feet or Albers meters), the shapefile that is created is stored in the same projected units as these existing data sources. The spatial data that you create will only align correctly with themes based on data sources that are stored in the same projection (e.g. state plane).

Creating a Point Theme: ArcView allows you to create three types of theme point, line or polygon. If your data consists of features too small to be depicted as lines or polygons, then you should create a point theme. Apiary locations will be used to create a point theme.

Creating a Polygon Theme: Polygon features represent areas such as parcels, land use zones, forest stands, etc. CACs wishing to develop their own "crop" layer will need to create polygon themes. CACs that have already begun this process (Kern and Fresno) have recommended that each shapefile layer should contain no more than 2,000 sites, and that counties with more sites than this should plan to divide their mapped areas into two or more districts. Existing spatial data, such as parcel boundaries or street centerlines, as well as aerial imagery will be shown to provide valuable information on which to build a new theme.

Setting a Snapping Environment: Before adding new features, you should decide whether the features you create should meet and align perfectly. If it is important not to have gaps or overlaps, a snapping environment should be set up so that features you add "snap" to existing features in the theme. Two types of snapping are available in ArcView, general snapping and interactive snapping. Interactive snapping gives better control over how features get snapped, as it allows the user to apply different snapping rules on a per vertex basis. The value of establishing a snapping environment if you are building a theme from a copy of pre-existing parcel or centerline data will be demonstrated.

Making Changes and Updates to Spatial Data: You can set attribute update rules to specify how data in the theme's attribute tables is handled when you split or merge (union) polygons. These rules can be applied to each field in the attribute table. However, you will probably need to edit certain values, such as a site id, manually through the theme's table document.

There are a number of ways in which a user can customize ArcView, including the use of Extensions and Avenue scripts.

Extensions Extensions are add-on programs that provide you with specialized GIS functionality on an on-demand basis. ArcView comes with several extensions, including a digitizer extension, a buffering extension and an advanced labeling extension. In addition, you can purchase additional extensions, such as the ArcView spatial analyst, or use those written by other users such as DPR's Image Navigator Extension. When you load an extension, ArcView's user interface changes to reflect the functionality available in the extension. DPR's Image Navigator extension will be demonstrated.

Customizing ArcView's Graphical User Interface: The look and functionality of ArcView's GUIs can be changed to suit individual applications. Some changes, such as removing some of ArcView's functionality, rearranging menus, buttons, and tools, and changing button and tool icons, will be made to the GUI using the ArcView's Customize interactive dialog feature.

Using Avenue Scripts to Create New Functionality: ArcView can be further customized using its object-oriented programming language Avenue. ArcView is shipped with a variety of ESRI written sample scripts which can be easily incorporated into a project. The creation of new menus, buttons and tools will be demonstrated with scripts written by ESRI and DPR. The session will conclude with the creation of a simple Avenue script to demonstrate script editor functionality.

References:

Getting to Know ArcView GIS. 1996. ESRI. Published by GeoInformation Internation.
ISBN 1 86242 019 X.

Using ArcView GIS. 1996. ESRI. ArcView GIS Software Documentation.