- GPS are becoming very effective tools for GIS data capture.
- The GIS user community benefits from the use of GPS for location data capture in various GIS applications.
- The GPS can easily be linked to a laptop computer in the field, and with appropriate software.
- Thus GPS can help in several aspects of construction of accurate and timely GIS databases.
- GIS is about “What”? For example, "what" is the object or objects which will be mapped.
- These objects are referred to as "Features“ and are used to build a GIS.
- It is the power of GPS to precisely locate these Features which adds so much to the utility of the GIS system.
- On the other hand, without Feature data, a coordinate location is of little value.
Types of Features which can be Mapped in GIS
There are three types of Feature which can be mapped:
- Lines and
A Point Feature is a single GPS coordinate position which is identified with a specific Object.
A Line Feature is a collection of GPS positions which are identified with the same Object and linked together to form a line.
An Area Feature is very similar to a Line Feature, except that the ends of the line are tied to each other to form a closed area.
Categories of descriptions for a Feature are known as Attributes of that feature.
- Attributes can be thought of as questions which are asked about the Feature. For example the Attributes of the Feature "house" would be "color", "size", "cost" and "occupants".
- A Feature is the object which will be mapped by the GPS system. The ability to describe a Feature in terms of a multi-layered database is essential for successful integration with any GIS system.
- For example, it is possible to map the location of each house on a city block and simply label each coordinate position as a house. But the additional information such as color, size, cost, occupants, etc. will provide the ability to sort and classify the houses by these categories.
- Logically, each question asked by the Attributes must have an answer.
- The answers to the questions posed by the Attributes are called Values. In the example above, an appropriate Value (answer) for the Attribute (question) "color" may be "blue".
The following table illustrates the relationship between Features, Attributes and Values:
By collecting the same type of data for each house which is mapped, a database is created.
- The Feature List is a database which contains a listing of the Features which will be mapped, as well as the associated Attributes for each Feature.
- Feature List also contains a selection of appropriate Values for each Attribute.
- When a Feature List is used in the field, the first step is to select the Feature to be mapped. Once a Feature is selected, the Attributes for that Feature are automatically listed. A Value for each Attribute can then be selected from the displayed list of predetermined Values.
- Objective of making a feature list: To simplify the data entry process.
Exporting to a GIS System:
- The final step in integrating GPS data with a GIS system is to export the GPS and Feature data into the GIS system. During this process, a GIS "layer" is created for each Feature in the GPS job. For example, the process of exporting a GPS job which contains data for House, Road and Lot Features would create a House layer, a Road layer and a Lot layer in the GIS system. These layers can then be integrated with existing GIS data.
- Once the GPS job has been exported, the full power of the GIS system can be used to classify and evaluate the data.