DeLorme Professional Weblog

The Field Creation dialog box is among the most powerful components of the GIS tab in XMap. Admittedly, it is quite difficult to find this tool, but if you click the Design View button in the Attributes tab, you’ll see an Options menu that contains several field management tools including Add Field… Sooner or later, most XMap GIS Enterprise or Editor users will encounter a situation that requires that they visit this area of the software.

The basic function of the Field Creation dialog box is to generate a new field or column of attributes for an OpenSpace GIS layer. For instance, if you import a shapefile containing local property polygons, you may need to add a field that allows you to include information on the value of each property, or if you download waypoints from the Earthmate GPS PN-20 and import them into the GIS tab, you will likely need to use the Field Creation function to assign the appropriate data to each collected location.

There are two approaches to creating a new attribute field: you can either create an empty field that allows you to manually type the required information for each object, or you can build a formula that creates data from your existing data fields. An example of the latter would be if you want to convert the values in the area field for a polygon layer from square kilometers to acres.

 In either case, the initial steps for creating a new field are the same:

• Open the Field Creation dialog box in the attribute Options menu as noted above.
• In the Field Name area, type a name for your new field.
• Select a Data Type from the drop-down list.  The most common type selections from this list are String, Integer, and Float (a numeric field-type that allows decimals). It is important that the appropriate consideration is given to this selection as a new data value cannot be typed into an incompatible field. For instance, you cannot enter alphabetic characters into an integer field. Also note that if you need to create a range classification based on the new field, the field-type must be one of the numeric options. For more information on the other data-type options, refer to the help documentation within XMap.
• If appropriate, select the String Size, which determines how many characters the new field will accommodate.
• If you need to create an empty field, simply click the OK button and return to the Datasheet View to enter the necessary data. 

The additional components of the Field Creation dialog box control the development of a formula that can be applied to one or more of your existing fields to create new data. To simplify the process, a selection of preformatted functions is provided in the window on the right side of the dialog box. As each function is highlighted, a brief explanation of the resulting formula is displayed at the bottom of the window. To build a formula based on one of these functions, double-click the function name to automatically add it to the Formula window.

The window on the left side lists all of the current attribute fields for the selected OpenSpace layer. After highlighting the appropriate section of a formula, double-clicking the required field will automatically add it to the formula.

For example, if you choose the AVG(field) formula to generate a new field containing the average property values, highlight the “field” statement in the formula and double-click  the existing property values field to add it to the formula. The new formula will read like this: AVG([Property Value]).

 The Formula window can also be used to manually create a formula. For example, to create a new field that converts the existing Area value in square kilometers to acres, type the following into the formula window: [Area*247.1054].

 For new fields that have been created using a formula, modifying, deleting, or updating the original fields that were used in the formula will alter the values or text that appear in the new field.

 For more information on this or any other XMap function, refer to the Help Topics or click the User Guide link in the software’s Help menu.