An overview of tables and attribute information
Last modified December 18, 2007
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Tabular information is the basis of geographic features, allowing you to visualize, query, and analyze your data. In the simplest terms, tables are made up of rows and columns, and all rows have the same columns. In ArcGIS, rows are known as records and columns are fields. Each field can store a specific type of data, such as a number, date, or piece of text.
Feature classes are really just tables with special fields that contain information about the geometry of the features. These include the Shape field for point, line, and polygon feature classes, and the BLOB field for annotation and dimension feature classes. Some fields, such as the unique identifier number (ObjectID) and Shape, are automatically added, populated, and maintained by ArcGIS.
ArcGIS allows you associate records in one table to records in another table through a common field, known as a key. You can make these associations in several ways, including by joining or relating tables temporarily in your map or by creating relationship classes in your geodatabase that maintain more permanent associations. For example, you could associate a table of parcel ownership information to the parcels layer, since they share a parcel ID field.
Learn more about joining and relating tables
Learn more about choosing between joins, relates, and relationship classes
There are lots of sources of tabular data and ArcGIS can take advantage of many formats. Tabular information could be stored as tables in folders or databases, text files, queries on databases, and so on. In addition, if you have spatial data, you probably already have tabular attributes that describe those geographic features.
File-based tables are stored in folders on disk. Some examples of file-based sources of tabular information include:
There are many mapping, analysis, and data management tasks you can perform using tabular data.
Tables allow you to map and visualize your data. For example, you can classify or categorize attributes to symbolize a layer. You can use population values to symbolize major cities with a larger symbol than used for smaller towns and villages. You can also specify that a different color be used to represent each type of land use in a parcel layer. In addition, you can also use the attribute values to generate text to label each parcel feature. In the graphic below, the parcels are symbolized by the type of land use, then labeled with their parcel ID values.
Attribute data helps you perform spatial queries and analyses. For example, you can examine the distribution of features with certain attributes by asking ArcMap to select the features that contain the attributes you want to examine. In the graphic below, the features with a LAND_USE of UNK (unknown) are selected using an attribute query.
When information in your geodatabase changes, you can update your attributes. For example, you'll need to update your database when land uses or property ownership changes—or the unknown values are classified. If you have a feature class representing some pipes with a field for the diameter, you can easily change the attributes when the crew removes an eight-inch|and replaces it with a six-inch pipe. You can edit tabular values either within the table window or the Attributes dialog box, which shows attributes of only individual selected features.
The geodatabase includes functionality that allows you to enhance, maintain, and enforce the integrity of your tabular data. For example, by establishing attribute domains, you can set up rules that specify the valid values for the records in your table. So, when updating the|diameter attributes, you can use attribute domains to ensure that the diameter is appropriate for that section of pipe. Range domains, for example, ensure that the values you enter are within a valid range. The graphic below shows the use of coded value domains when editing, which allows you to choose a value from a predefined list and avoid making typographic errors.
ArcGIS also allows you to convert data in a table into spatial data. For example, one of the most common data sources is a list of coordinates obtained from using a GPS unit in the field. You can easily add such x,y data to ArcMap to display it. The graphics below show a text file containing the x,y locations of hydrants (top graphic), then the points displayed in ArcMap on the map and in a table window (bottom graphic).
Learn more about adding x,y data as a layer
If you have a list of addresses, you can use geocoding to match them to known street locations to create point features. In addition, through linear referencing, you can indicate events along line features with just an identifier and a location.
Learn more about geocoding
Learn more about linear referencing
Tables are also at the root of data models, which are templates that you can use to set up your geodatabase to better model real-world phenomena.
Learn more about data models