278
A. Simms
creating digital abstracts of the real world
effectively handling of these data
providing new insights into the relationships of or among spatial variables
and
4) creating summaries of these relationships (Berry, 1993)
The data structure used to store spatial data will determine how the data can be encoded,
analyzed and displayed. There are two basic data structures raster and vector. Vector
data structures use discrete (x, y coordinates) points or line segments to represent spatial
objects such as points, lines or polygons. Raster structures subdivides the area into a
regular grid of cells (rows and columns), and these cells are used to represent point,
lines or polygons (Berry, 1993). The location of vector objects are viewed as precise
where each object is given an explicit X and Y coordinate. The grid cells of a raster
structure provide approximate or implied location of an object. For example, if the grid
cells of a raster map is 25 x 25m then the location accuracy of an object is said to be ±
25m.
A more important factor when selecting a vector or raster data structure is the
implications on the encoding, storage, analysis and display. Generally, vector data
structures are used for inventory, descriptive queries, spatial database management, and
computer mapping. Raster structures are used for prescriptive analysis, spatial statistics
and modeling (Berry, 1993). GIS applications for aquaculture require both structures,
and ideally the system used for analysis would provide the advantages of both vector
and raster data structures. The Burgeo field data are stored initially as vector data and
converted to raster as needed. In this study, vector and raster GIS capabilities are
provided by ArcView™ 3.0 and its Spatial Analyst 1.0 module (ESRI, 1996).
Data Collection
The data used in this study can be divided into primary and ancillary databases. Primary
data include all field data such as clam biology, hydrology, water quality and landuse
(Table 1). The 1:50,000 digital topographic maps and scanned aerial photographs are
considered ancillary data.
1)
2)
3)
A. Simms
creating digital abstracts of the real world
effectively handling of these data
providing new insights into the relationships of or among spatial variables
and
4) creating summaries of these relationships (Berry, 1993)
The data structure used to store spatial data will determine how the data can be encoded,
analyzed and displayed. There are two basic data structures raster and vector. Vector
data structures use discrete (x, y coordinates) points or line segments to represent spatial
objects such as points, lines or polygons. Raster structures subdivides the area into a
regular grid of cells (rows and columns), and these cells are used to represent point,
lines or polygons (Berry, 1993). The location of vector objects are viewed as precise
where each object is given an explicit X and Y coordinate. The grid cells of a raster
structure provide approximate or implied location of an object. For example, if the grid
cells of a raster map is 25 x 25m then the location accuracy of an object is said to be ±
25m.
A more important factor when selecting a vector or raster data structure is the
implications on the encoding, storage, analysis and display. Generally, vector data
structures are used for inventory, descriptive queries, spatial database management, and
computer mapping. Raster structures are used for prescriptive analysis, spatial statistics
and modeling (Berry, 1993). GIS applications for aquaculture require both structures,
and ideally the system used for analysis would provide the advantages of both vector
and raster data structures. The Burgeo field data are stored initially as vector data and
converted to raster as needed. In this study, vector and raster GIS capabilities are
provided by ArcView™ 3.0 and its Spatial Analyst 1.0 module (ESRI, 1996).
Data Collection
The data used in this study can be divided into primary and ancillary databases. Primary
data include all field data such as clam biology, hydrology, water quality and landuse
(Table 1). The 1:50,000 digital topographic maps and scanned aerial photographs are
considered ancillary data.
1)
2)
3)