Most of the data to be handled in a GIS is a spatial data is a geographic data-oriented, have a particular coordinate system as the basic reference and has two essential parts that make it different from other data, the location information (spatial) and descriptive information (attributes) that described below:
- Location information (spatial), corresponds to a coordinate either geographic coordinates (latitude and longitude) and the XYZ coordinates, including the datum and projection information.
- Descriptive information (attributes) or non-spatial information, a location that has some information related thereto, for example: type of vegetation, population, area, zip code, and so forth.
Format and Spatial Data Sources
In a simple format in the form of computer language and code storage means different data between files with one another. In GIS, spatial data can be represented in two formats, namely:
Data vector is represented in the form of the earth into a collection of lines, area (the area bounded by a line that begins and ends at the same point), and point nodes (the point of intersection between two lines).
Raster data is the data generated from the system of Remote Sensing. On raster data, geographic object is represented as a grid cell structure called a pixel (picture element).
On raster data, the resolution (visual definition) depends on its pixel size. In other words, describe the size of the actual pixel resolution in the earth's surface represented by each pixel in the image. The smaller the size of the Earth's surface is represented by a single cell, the higher the resolution. Raster data is very good to represent the limits of the change gradually, such as soil type, soil moisture, vegetation, soil temperature and so on. The main limitation of raster data is the large size of the file; the higher its resolution grid, the greater the file size and highly dependent on the hardware available Capacity.
SIG is one of the requirements of spatial data, which can be obtained from several sources, among others:
Analog maps (including topographic maps, soil maps, etc.) that maps in printed form. In general, analog maps made with cartographic techniques, are likely to have such a reference spatial coordinates, scale, cardinal directions and so forth. In stages as the purposes of GIS data sources, map analog converted to digital maps in raster format to be converted into vector format via dijitasi process so as to show the actual coordinates on the surface of the earth.
- Remote Sensing Data Systems
Remote Sensing Data (such as satellite imagery, aerial photographs and so on), is the most important data sources for GIS because ketersediaanya periodically and cover a specific area. With a variety of satellites in space with their respective specifications, we can obtain various types of satellite imagery for various purposes of use. This data is usually represented in raster format.
- Field Measurement Results Data
Field measurement data generated by a separate calculation technique, in general, this data is a source of attribute data eg administrative boundaries, land ownership boundaries, parcel boundaries, limits of forest concessions and others.
- Data GPS (Global Positioning System)
GPS technology provides an important breakthrough in providing data for GIS. The higher the accuracy of GPS measurements to the development of technology. This data is usually represented in vector format. Discussion of the GPS will be explained hereinafter.
Data Acquisition Method / Geographic Information
- Field survey: physical measurement (land marks), sampling (water pollution), non-physical data collection (data social, political, economic and cultural).
- Census: the approach of questionnaires, interviews and observations; national data collection and periodic (census population, census of land holdings).
- Statistics: the periodic method of data collection / per-interval-time at the station of observation and analysis of the geographic data, eg rainfall data.
- Tracking: a way of collecting data in a particular period for purposes of monitoring or observation of the changes, eg, forest fires, volcanic eruptions, river water discharge.
- Remote sensing (remote sensing): a science and art to obtain information of an object, area or phenomenon through the analysis of sensor data obtained from observers without direct contact with the object, area or phenomenon observed
