Geography Reference
In-Depth Information
Date and time, time interval: Because of the unique ways for storing date
and time, most database systems offer separate data types for recording
date, time, and, in some cases, time interval.
Simple large objects: Any kind of data (including images, word processor
files, and spreadsheets) can be stored in a database as a simple large
object as binary data. Because this data type is most often used to store
binary data, especially images, it is often called Binary Large Objects
(BLOBs).
An important issue to consider practically when creating a database is
specifying the length of each field, also called “precision.” If the field is too
long, the database may require a great amount of computer storage space. If
it is too short, attributes may be truncated (cut off) possibly making it impos-
sible to know what the attribute actually records.
Data Storage and Applications
Considerations in designing a geographic representation or cartographic
representation are the main factors determining how data is stored in a data-
base. The available data types and the allocation of storage for attributes
also play important roles. If the geographic information or map should show
demographic characteristics of an area, most of the data will be stored in
integer format. Data showing ratios will require f loating-point fields. Text-
type fields can be added for notation. For an application modeling erosion
processes, the data will also be mainly numbers, but the types of observa-
tions and analysis will require mainly f loating-point data types. Of course, if
the geographic representation has led to personal addresses stored in a sin-
gle field as a character string, it will be very difficult, possibly even impossi-
ble, to identify only those people in the database that live on Main Street.
The application type should guide practical considerations of which
data types should be used in analysis and communication. For many pur-
poses, observations and data recorded in numerical formats are the most
flexible. They can be transformed and analyzed with other numerical data.
Character strings are useful for recording the names and designations of
things and events; BLOBS are usually used for images; data and time data
types are used to record when things were recorded or events took place.
Entities and Relationships
A key part of working with databases is creating a data model that accurately
and correctly shows things or events and their relationships. The clarity of
this data model is important for others who need to understand the geo-
graphic representation and cartographic representation, or perhaps just the
data model. A data model should describe each entity and the attributes that
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