Attribut Data - Lecture Material - Completely GIS dan Remote Sensing tutorial - facegis.com
Attribut Data
Non-spatial attribute data refers to attributes (i.e. "what is it") that do not represent the locational information of the feature(s).  We will look at how this data is stored and two functions (join & relate) used to connect two or more data sets. Data attributes correspond to the three types of classification recognised in cartography: nominal, ordinal and interval.

Table 8-1 : Types of non-spatial attributes 

TYPE DATA  EXAMPLE 
'Text' Nominal  Pine, Spruce, NDP, Lib 
 Real (float)
 Interval
 3.69   4.128    3.0
Integer  Nom/Ord/Int  1, 2, 3, 4, 5 ... 10000.. 
 Date Interval
 31/01/2005

Notes:
Text is case-sensitive: 'Pine' and 'pine' are as different as 'pine' and 'larch'
Integers can be short (16 bit) or long (32 bit)
Float can be single or double (precision)
Most queries and analysis relies on the presence of attribute information (e.g. how much pine?)


1.  Attribute Tables

  • Attributes are stored in an Attribute Table.
  • Every vector layer MUST have an associated table *
  • These are linked to spatial data by a feature code number ('id').
  • Attributes are stored in columns as 'items'
  • Rows display the attributes for each feature and are known as 'records'
  • Queries can be based on records (what is here?), or items (how often does this occur?)
 Table 8-2
 
 Record
ITEM 1
(e.g. name) 
ITEM 2
(e.g. age) 
ITEM 3
(e.g. height, cm) 
I.D. # 
 1
Spruce
50
30 
 2
Pine 
10
2
 3
Aspen 
20 
10 
3

The topological data structure associated with 'coverages' is linked to three  types of geographic features and their minimum required items are:

a. Point Attribute Tables:      Record#     Length     Area     ID#                                (all lengths and areas = 0)
b. Arc Attribute Tables:        Record#     StartNode    EndNode     Length     ID#     (lines and polygon outlines)
c. Polygon Attribute Tables:  Record#     Area     Perimeter     ID#                           (includes a centre label point) <>

Raster layers have a single attribute, sometimes listed as its 'value'

2. Join & Relate Operations

    <> Attributes may be stored in attribute tables or ... Separate tables can be 'joined' or 'related'.
Join:   this function allows us to merge two tables using a common item. In most cases, the values in one tables item set must be identical to those in the other
Relate: this function temporarily connects two tables. As with join, a common value is needed.  Relate has some advantages over join:
    • Reduced redundancy between tables.
    • Relates are preferred in large databases to prevent tables becoming too unwieldy, with many items.
Join and relate can be done on the basis of:
  • One to one (one record matching one record on both files) or
  • Many to one (one record values is matched to several records on the other file).


Table 8-3 : This table could be joined to the first
feature attribute table using the common attribute of I.D. #.

I.D. #
Drainage
1
Wet
2
Medium
3
Dry

<>Table 8-4 : Finished Product: Joined Table
Record
ITEM 1
ITEM 2
ITEM 3
I.D. #
Drainage
1
Spruce
50
30
1
Wet
2
Pine
10
5
2
Medium
3
Aspen
20
10
3
Dry

Spatial operations based on attribute table information
The above are examples of joining attribute tables information.
Spatial data features can also be matched (across map sheets) by a common attribute, e.g. segments of a highway or river.
A continuous line cann be 'segmented' by an attribute change at a 'pseudo-node'
Polygons can be dissolved based on a  common attribute.


 3. Attribute Modification

  • Creating new files
  • Adding or changing data
  • Displaying data
  • Extracting data (and out to a new dataset)
  • Manipulating data: add columns, drop columns

4. Attribute Information Storage and Import

Some GIS use internal databases; others use external databases
(e.g. ORACLE, SYBASE, INFORMIX, MS-ACCESS)

In both cases, they should be able to import attribute data from common formats:
e.g.  ASCII text files (.txt or .csv - comma separated values) and Dbase format (.dbf)

 

Source: http://www.gis.unbc.ca/courses/geog300/lectures/lect21/index.php