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User:Mav/Introduction to GIS notes by maveric149/2002-03-12 Lecture

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Introduction to GIS notes by maveric149 2002-03-12 Lecture

Attribute data input and management

spatial and attribute data are different

  • spatioal data realtres to the geometry of map heatures (how points, lines ploygons are related)
  • attribute data are stored in tables with each row of the table representing a map feature and each column a characteristic.

Spatial data editing[edit]

two kinds of relational database models

  • georelational data model - spatial data are stored in one table and attibute date stored in another. related by a common feature.
  • object-oriented data model - distinguishes between spatial and attrit data, but keeps both spatial and attribute data in the same data.

Linking attribut to spatial data[edit]

  • each map feature has a unique label ID
  • attribute data are sored in the feature attribute table
  • rows = record of (tuples)
  • columns = fields (items)

Multiple tables[edit]

Most GIS tables have many attiributes. The alternative is to store different layers of attributes in separate fiedls managed by a database management system (DBMS).

Attribute data types[edit]

data type must be specified for each field of an attribute table. : character strings, integers, real numbers dattes, time intervals.

Attirbute data types[edit]

  • Nominal = labels used for ID purposes only
  • Ordinal = labels imply a ranking relationship
  • Interval = labels that specify the intercal between calues. (addition and subtraction are meaningful)
  • Ratio = interval data for which an absolute zero in specified. All math functions meaningful.

Retational databases[edit]

  • Flat files - one large table (many fields)
  • Hierarchical - data organized at different levels and uses a on to many association between levels.
  • Network - linkages built across data tables
  • Relational - a collection of tables (or realtions) connected to each other by keys (one or more attriutes that uniquely ID a record in a table; a key common to two tables can connect the corresponding records across tables.
  • Tables remain separate until a query is asked requiring attribute data from different tables.


Taking a flat file and decomposing it into several small tables to achieve the following objectives:

  • to avoid redundant data that waste space and may cause data integrity problems
  • To ensure that attributes in separate tables can be maintained and updated spearately and linked only when needed.

Types of relationship[edit]

none to one, many to one, one to many

one to one[edit]

one and only one record in the destination table.

one to many[edit]

one record in the desination table may be related to more than one rocrd in the source table.

many to one[edit]

more than one roeco in the desination table may be related to a field.