Tutorial ArcGis: Working with Tables Part1

However, this information can be independent of the data stored in an information layer.

To access the attribute table in ArcMap, just click with the right mouse button on the name of the layer in the table of contents of the map document and select the Open command Attribute Table. 

In ArcCatalog, just select the source file data and to view content in the Preview tab.

Each layer shown in the table of contents of the ArcMap document has a single table containing all the attributes associated with the features in the layer.

Each entity is associated with one record

An attribute table consists of fields (columns) and records (or rows) that contain the attributes associated with an entity of the data set.

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Link entities and attributes

When storing geographic objects in a feature class or a class set of entities, each entity is assigned a unique ID number and is characterized by a position in space and corresponds to a single record in the table. 

Although the name of the identifier may be different depending on the data format, it is important to understand the relationship of one to one uniting the entity, its identifier, and record in the attribute table.

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Understanding the structure of a table

• Table Database Properties:

            -Recording (line) and field (column)

• Different types of fields:

            -Single field name

Each table is built on a single model: an assembly of rows and columns.

At the intersection, a row and a column is a value characterizing an entity.

The basic properties of a table
Some tables have a number of defined fields. For example, a polygon coverage has four default fields: area, perimeter, cover, and cover-id #. Other tables contain only user-defined fields. This is the case of the table shown in the Example below above. 

ArcGIS automatically adds a field named FID when displaying values. 

This field does not physically exist in the data source file but can be used like any other column to query.

The number of fields stored in a table is not limited, however, each field name must be unique. 

Against two fields can store the same data in two different forms.

Generally, the most commonly used values are numbers, strings, or dates. 

Some tabular formats ArcCatalog and/or ArcMap can manage fields short integer, long integer, real simple, double real, text, date, identifying, and blob fields.

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Different types of fields

The tables are capable of storing information such as dates, numeric, string... Choosing the right type of field is an important operation since each field type is a number of rules. The formats supported by ArcCatalog are:

short integers (2 bytes /octets) de –32767 à 32767 (de -215 à 215 )
long integers (4 bytes /octets) de –2 147 483 648 à 2 147 483 647 (de -231 à 2 31)
Simple real or floating (4 bytes /octets) de 1,401298*1045 à 3,402823*1038
real double (8 bytes /octets) until 1.79769313486232*10
Text (10 bytes /octets + nb characters) Jean Bono (19 bytes/octets)
Date (8 bytes /octets) 10/05/2001/login/Blob
Integer (we keep a bit for the sign, for the other 15 significant digits)
mini -32768 =>1 1111111 11111111 1x(-1) x ( 1x215 + 1x214+1x213+… .+1x20)
maxi 32768 => 0 1111111 11111111 0x(-1) x ( 1x215 + 1x214+1x213+… .+1x20)
1 bytes/ octet 2 bytes/ octet
Other types of controls may be available depending on the software which has generated the data (Access, Oracle ...).

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Different tabular formats

• Each ArcGIS spatial format has its own native format attribute data

          -Files INFO (Cover)
          -DBase files (file types)
          -Table of geodatabases (RDBMS)
          -External Tables via ODBC / OLE DB

• We can associate to a source of spatial data in any format of attribute data

• The ArcGIS tools used to perform format conversions

Choosing the right field format to store information is an important step in the creation stage of databases and can dramatically change the treatment and access to databases.

Each spatial data format has its own tabular data format

ArcGIS can use different sizes of fields in storage and information management allottees.
Each spatial data format has its own tabular data format. 

The use blankets INFO tables to store attribute information; shapefiles ArcView store attribute data in files in dBase format; geodatabases store all information in RDBMS tables (Access or Oracle for example).

Certain spatial data formats can be associated with various tabular formats.

Some formats, such as covers, can be associated with independent tables.

ArcGIS has formats conversion tools

To facilitate information sharing, ArcGIS has tools for converting the fields of a type to another.

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manipulating table

From ArcMap or ArcCatalog, it is possible to perform sorting, research, selection or gel values. ArcCatalog lets you create new tables, new fields or delete existing columns.
ArcMap lets you change the values in a table using the calculator field values.

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histograms distribution

After creating a selection, it is possible to calculate simple statistics on a values field. These statistics to quickly visualize and evaluate a selection.

Statistics

Select the command Statistics from the dropdown menu option to display the window Statistics in which you can view statistics calculated values on any numeric field of the table.
When you select the field containing the values of all following statistics are displayed in the window and you may see the histogram distribution.

The types of statistics

• Total workforce)
• Minimum
• Maximum
• Sum
• Average
• Standard deviation

If no line is selected in the table, the statistics that appear concerned all lines chosen field.