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)

Multiple tables

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.

Retational databases

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

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.