User:Mav/Introduction to GIS notes by maveric149/2002-03-12 Lecture
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.
Normalization
[edit]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.