GIS/attributes

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Attributes are non-spatial characteristics that describe spatial entities. Attrubutes are commonly arranged in tables where a row is equivalent to one entity and a column is equivalent to one attribute, or descriptor of that entity.

(picture of data table)

Typically, each row relates to a single object in a spatial data model. It is also typical for each object to have multiple attributes that describe the object. All attributes are often displayed in a table format. Attributes can be stored on a computer using a flat file format or in a database management system.

For example, consider that we have a spatial data model that stores the location of fire hydrants. In order for each object to represent a fire hydrant, we would need to store their positions. In addition to positional information, we would also store attributes that would describe those fire hydrants.

(Image of fire hydrant)

In this example, we are storing color, service date, and flow as three attributes that describe this particular fire hydrant at this particular position on Earth. The position, color, service date, and flow will be stored as one row in an attribute table that will contain four columns because there are four descriptors for this fire hydrant.

Computer representations

Computers fundamentally "think" differently than humans. While humans see numbers, letters, pictures, and sounds, a computer only sees zeros and ones, which is known as binary data. Therefore, we need a way to translate the numbers, sounds, and videos, as humans know it, to a form in which a computer can understand and store the information.

Computer scientists have created data structures that can be used to translate our information into a format which a computer can store in its memory. This data structure is known as a data type.

There are four typical data types that we use in GIS:

In order to use the computer's memory most efficiently, it is important that we specify which data type we are going to use to store information in the computer's memory. It is important to let the computer know which operations are allowed for each data point stored in that memory location using a specific data type.

Key Facts

Attribute Data Types

There are four typical data types:

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