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Lecture 9

Attribute Data Management (from lecture 9)

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Department
Geography
Course
GGR272H1
Professor
Raktim Mitra
Semester
Fall

Description
Ggr272 chapter 8: Attribute data management - GIS involves spatial and attribute data: o Spatial data relate to the geometries of spatial features o Attribute data describe the characteristics of the spatial features - For example: attribute data such as street names, address ranges and postal codes are associated with each street segment in the TIGER/Line files - Georelational data model stores spatial data and attribute data separately and links the two by the feature ID o The two data sets are synchronized so that they can be queried, analyzed and displayed in unison - Object-based data model (e.g. geodatabase) combines both geometries and attributes in a single system - Raster data model is different; each cell value corresponds to a value of a continuous feature at the cell location o Only an integer raster has a value attribute table that summarizes cell values and their frequencies 8.1 Attribute Data in GIS - Attribute data store in tables and organized in rows and columns - Each row represents a spatial feature and each column describes a characteristic and the intersection of a column and a row shows the value of a particular characteristic for a particular feature - A row is also called a record and a column is also called a field 8.1.1 Type of Attribute Table - Two types of attribute tables o Feature attribute table  Has access to the feature geometry  Every vector data set must have a feature attribute table  In the case of the georelational data model, the feature attribute table uses the feature ID to link the feature’s geometry  In the case of the object-based data model, the feature attribute table has a field that stores the feature’s geometry  Feature attribute tables also have the default fields that summarize the feature geometries such as length for line features and area and perimeter for polygon features o Non-spatial  Table does not have direct access to the feature geometry but has a field linking table to the feature attribute table whenever necessary  Files may exist as delimited text files, dBASE files, Excel files, Access files, or files managed by database software packages such as Oracle, Informix, SYBASE, SQL Server, and IBM DB2 8.1.2 Database Management o Database management system (DBMS): to manage attribute and nonspatial data tables o A DBMS provides the tools for data input, search, retrieval, manipulation and output o ArcGIS Desktop uses Microsoft Access for managing personal geodatabases o Developed to facilitate the sharing of data in an orderly manner and to ensure that the integrity of the database is maintained o Object-based data model such as geodatabase has actually blurred the boundtary between a GIS and a DBMS: good geodatabase stores both geometries and attributes as tables in a single database o GIS packages also have database connection capabilities to access remote databases 8.1.3 Type of Attribute Data - Data type will determine how an attribute is stored in a GIS - Common data types are number, text, date, binary large object (BLOB). o Numbers: integer (without decimal digits) and floats (for numbers with decimal digits)  An integer can be short or long and a float can be single precision or double precision o BLOBS store images , multimedia, and feature geometrics as long sequences of binary numbers - Attribute data can also be defined by measurement scale o Categorical data  Nominal  Categories (e.g. land use types or soil types)  Ordinal  Differentiate data by a ranking relationship (e.g. soil erosion may be ordered from severer to moderate to light) o Numeric data  Interval  Have known intervals between values (e.g. temperature)  Ratio  Same as interval except the ratio data are based on a meaningful, or absolute, zero value (e.g. population densities) - Character strings are appropriate for nominal and ordinal data - Integers and floats are appropriate for interval and ratio data 8.2 The Relational Model - a database is a collection of interrelated tables in digital format o four types of database designs (Fig. 8.6)  flat file  contains all data in a large table  hierarchical  organizes data at different levels and uses only the one-to-many association between levels  network  builds connections across tables, as shown by the linkages between the tables in Figure 8.6.  A common problem with both the hierarchical and the network database designs is that the linkages between tables must be known in advance and built into the database at the design time. This
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