Manipulation of Fields and Attribute Data: Creating Using Classification, Computation, Entering and Verification (Especially for GATE-Geospatial 2022)

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The fundamentals of manipulating and summarizing attribute data in a geographic information system will be introduced in this project. For this, you will join tables and add and populate fields to create thematic maps that show:

Manipulating Attribute Data

Database management tasks involve tables as well as fields and field values in tables. Field management includes adding or deleting fields and creating new attributes through classification and computation of existing attribute data.

1. Adding and Deleting Fields

We regularly download data from the internet for GIS projects. Often the downloaded data set contains far more attributes than we need. It is a good idea to delete those fields that are not needed. This not only reduces confusion in using the data set but also saves computer time for data processing.

  • Deleting a field is straightforward.
  • Adding a field is required for the classification or computation of attribute data. To add a field, we must define the field in the same way as for attribute

2. Classification to Create Attribute Data

New attribute data can be created from existing data through data classification. Based on an attribute or attributes, data classification reduces a data set to a small number of classes. Suppose you have a data set that describes the elevations of an area where you are conducting research.

Operationally, creating new attribute data by classification involves three steps:

  • First defining a new field for saving the classification result, selecting a data subset through query, and assigning a value to the selected data subset.
  • The second and third steps are repeated until all records are classified and assigned new field values, unless a computer code is written to automate the procedure.

3. Computation of Attribute Data

New attribute data can also be created from existing data through computation. It involves two steps:

  • First defining a new field, and
  • Second computing the new field values from the values of an existing attribute or attributes.

A simple example of computation is to create a new attribute called feet for a trail map that is measured in meters. This new attribute can be computed by “length” × 3.28, where length is an existing attribute.

4. Entering Attribute Data

Different methods for entering attribute data are available in PC Arc. The choice of a method is largely determined by the amount of attribute data to be entered.

  • Select a FAT, add one attribute item at a time, and update one record at a time.
  • Prepare a dBase file, and join the dBase file with a FAT using a key.
  • Use a user-friendly word processor to prepare a text file, convert the text file to a dBase file in PC Arc, and join the dBase file with a FAT.

ArcView allows the user to edit a theme table by adding a new field and its values. ArcView offers join and link for the user to relate tables.

Joining Excel Table - 1st Step
Joining Excel Table - 2nd Step

Attribute Data Verification

  • Check to make sure that label ID is unique and not contains null values.
  • Check the accuracy of attribute data.
  • Verification can be done by:
    • Print and check manually
    • Use validation rule such as in ArcGIS

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