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
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
- each map feature has a unique label ID
- attribute data are sored in the feature attribute table
- rows = record of (tuples)
- columns = fields (items)
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
data type must be specified for each field of an attribute table. : character strings, integers, real numbers dattes, time intervals.
Attirbute data types
- 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.
- 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
none to one, many to one, one to many
one to one
one and only one record in the destination table.
one to many
one record in the desination table may be related to more than one rocrd in the source table.
many to one
more than one roeco in the desination table may be related to a field.