GIS Database A GIS database includes data about

GIS Database • A GIS database includes data about geographic features: – Location (spatial data) • DMS, DD – Shape (spatial data) • point, line, polygon – Attributes (tabular data) • e. g. , population. characteristics

Spatial Data: Vector and Raster Formats (see Clarke, Ch 3. , Section 3. 3) • Vector – A data structure based on x, y coordinates • Population characteristics – (this is what we use with Arc. View • Raster – based on grid cells • Soil or vegetation characteristics – (used with Arc. Info and other software)

Importance of Topology (see Clarke, p. 86) • Topology: – The mathematically explicit rules defining the linkages of geographical elements – Describes adjacency and connectivity of features • Topological models: – A vector data structure that incorporates explicit spatial information about the relative locations of objects in the database (meta data)

Attribute Data • Information describing a map feature • Uses a relational data base or relational model – 1. Data is stored in tables – 2. Table have rows (records) and columns (fields) – 3. Tables are related to each other if they each have a field with a common type of information

Working with Tabular Data • Data is the foundation of any GIS project. • In Arc. View GIS, most data is stored in tabular format in theme attribute tables. • But data stored in other table files, as well as tab- and comma-delimited text files, can also be used in Arc. View projects. – (For more information on table formats, see Overview of data you can use in Arc. View in the online help. )

1. Selecting records • To get the most information from your data, you must know the process for selecting and querying table records. • When you select records in a table, you can work with specific groups or subsets of data.

Contd. . . • There are several ways to select records in a table using Arc. View GIS – Select tool – Find button – Query Builder dialog – Other useful buttons are: • ‘Switch selection’ button • ‘Promote’ button

More detail. . • Use the select features functionality on the view screen. – Ways to select features • use the Identify tool to click on features with the mouse • use the Select Feature tool and then open the feature’s theme attribute table. – use the Select Feature tool to draw shapes around features • use the Find button • select records in a theme table • Use the Query Builder dialogue to select features.

Writing queries • Use any combination of attribute values to select a set of features. – Queries that use multiple attribute values are referred to as complex query expressions. • Create an expression containing • • a field a connector (for example, and, or) an operator (for example, =, +, <) and a value.

More on Querying. . • Query expressions can also be used to define which theme features you want to display in the view. • If you do not want all features to display (which is the default) – open Theme Properties – for the Definition property • use the Query Builder to write an expression that selects the features you want displayed. This is called filtering theme data.

Generating Statistics for selected records • In Arc. View, click on a table field name and select Statistics from the Field menu to generate basic statistical information about selected records: – Minimum value, – Maximum value – Average (mean) value – Total value

Summarizing selected records • In Arc. View, the Summarize Button creates a separate table that contains the statistics for a field based on an attribute • To create a summary table: – select the records you want to work with and click on the attribute field that contains the data you want to summarize • Summary tables can be used to create charts and reports.

2. Working with fields and records • Records and fields can be manipulated in several ways using Arc. View – 1. Hide fields which are of no use for your project • in Table Properties dialog remove the checkmark in ‘Visible’ property – 2. ‘Alias’ a field • in Table Properties dialog type a new name (alias) in the field’s ‘Alias’ column • NOTE: field display changes are limited to the project in which they were made. – 3. Add a field • In Edit mode, choose ‘Add Field’

3. Accessing Tables • Tabular data doesn't have to be in a theme attribute table for you to edit it. • Arc. View supports many table formats: – d. BASE files – INFO files – tab- and comma-delimited text files

Joining tables • Two tables that have a common field may be joined • When tables are joined, fields and values from the source table are appended to matching records in the destination table • The joined table is a VIRTUAL TABLE which is saved when the project is saved • Joining can ONLY be used if table records have a one-to-one relationship • A record in the source table has only one matching record in the destination table

Linking tables • Similar to Joining but linked tables remain separate • MUST link tables when there is a one-tomany relationship between records in the tables • A record in one table has more than one matching record in the second table

Hot links • In Arc. View, a Hot Link connects documents (including photos and text files) to a theme feature • Creating a hot link: • Add a field to theme attribute table and enter the pathname of the hotlink as the field value • In Theme Properties dialog, set hot link properties – specify the name of the field that contains the hot link – specify the type of document theme is linked to