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 Vector
The core of an enterprise GIS Warehouse, vector data includes
GIS data with which users are most generally familiar. Roadways
depicted as lines, firestations as points and lakes and ponds shown
as polygons (areas) are just some examples of vector data representing real-life
features. In some software packages, vector data can have more complex
structure, such as measures along lines (i.e., roads), or areas
of polygon overlap such as animal habitat zones. But generally
vector data is a straight forward digital version of the lines that
define the shape or boundary of a map feature. Within the SDW,
vector data is stored as Geodatabase (GDB) feature classes and as shapefiles.
ArcInfo coverages are no longer maintained by KCGIS. Users are
guided by their GIS needs and GIS software as to which version to choose.
Most GIS data obtained from non-KCGIS data sources (i.e., external data) is stored only
as shapefiles, while KC-maintained data is stored in the GDB and
as shapefiles. ArcView 3.x users can access only shapefiles, while ArcGIS software
can use GDB featureclasses and shapefiles.Vector
data often store significant amounts of attribute data or details
about features in the data set, providing the real power in using
GIS for queries and analyses. What vector data generally does not
provide is any 3-D representation, as this format of data usually
describes only the map or 2-D view of the world.
 Lattice/Grid
Though there are some technical differences in these types, Lattice
and Grid, as well as the term Raster, can be used synonymously to describe
a data format that stores positional (horizontal) location information
in a row-column (Cartesian) structure, a highly efficient data storage,
access, and manipulation format. The individual row-column intersects
are called cells, grid cells, or in the case of imagery, pixels
(see below). Besides these functional advantages, grids or rasters
are designed to store attributes. Though some grids may store multiple
attributes just like vector data, grids usually store only a single
numerical value which can represent a range of real life values
such as biological sample data, rainfall amounts, or a gray or color-scale
value representing a picture element (i.e., pixel). One of the most
common applications of grids is where this numerical value, called
the Z value, stores a number representing elevation. This makes
grid data very useful for 3-D analysis and display when you have
the appropriate software. Grids and images share a common data model
so some grids, such as hillshades, can be displayed intelligently
as images in ArcView 3.x and other software. Others, like an elevation
grid, display as an image but do not provide much functionality.
Users with a strong demand for analyzing and manipulating grid data,
such as creating a shaded relief display, will require Spatial Analyst
or similar extensions to their GIS software.
 Image
- Images are really just a flavor of a grid or raster. Even though
there are multiple image types, when the term image is used in KCGIS
context, it usually means orthophotography (i.e., aerial or high-resolution
satellite imagery). Images store their positional, that is x, y,
location information in a pixel by pixel pattern just like grids,
but in this case the Z value is a number which is interpreted
by software as a shade of gray, as in a panchromatic image, or a
Red-Blue-Green color pattern as in color photography. The Z value
is just a number so it can be manipulated as in a grid, allowing
image analysis to be performed or imagery color or display characteristics
to be modified. Imagery provides a key cartographic role such as
orthoimagery serving as an up-to-date background to other vector
datasets. As King County builds a more complete image data library,
legacy imagery will become increasingly important in evaluating
change conditions. Because of the common usage of imagery in GIS,
most software supports a range of image file types such as TIF,
IMG, etc., with installed or no-cost extensions.
 TIN
(Triangulated Irregular Network). It is another format for
storing 3 dimensional data that has an x, y and z value. In the
case of a TIN the Z value is stored with links to adjacent nodes
so that the data more closely represents a continuous surface than
a grid or lattice representation. Like in a grid or lattice, the
Z value can represent any quantifiable value, but TINs are often
associated with storing and displaying elevation data. They are
somewhat specialized in that they require 3-D analysis and display
software such as ArcView or ArcGIS 3-D analyst. Because there is
a continuity relationship between all data formats, TINs can be
converted into grids and also in vector equivalents. However this
changes the way the data is modeled and usually involves some interpolation
of the data thus reducing the functionality of the TIN format. Even
though TINs generally store only a single Z value as an attribute,
the TIN format creates very large files as they store the relationship
between all the features within the data. TINs representing thousands
or millions of points are not uncommon and their resulting file
size limits TINs to a relatively small tile extent covering a limited
geographic area.
 ASCII
(American Standard Code for Information Interchange). Data in
this format is simply a line-by-line listing of information in text
format that takes on a geographical meaning when the listing contains
positional coordinate information. Text information can be easily
imported into most GIS and CAD-based software programs and it is
this flexibility that drives storing some point data sets in this
format. When possible most point data sets are stored as vector
datasets to make them more consumable to ArcView and ArcGIS software
packages. However, in the case of the elevation data that originate
as very large ASCII files, storage as vector point files is not
efficient for display and analysis, but the point data can be accessed
when necessary.
 DWG/DXF
Another flavor of vector data developed for and used extensively
in engineering CAD (Computer Aided Drawing) software. As the line
between GIS and traditional CAD software and data types continues
to blur, the industry has improved the compatibility, and thus sharing
of these data types. Drawing files (DWG) and the ASCII export version
(DXF) are broadly used to store planimetric linework such as roads,
water/sewer infrastructure, and legal description information by
public work agencies, survey departments and utility companies.
For GIS users this data is often converted to GIS-type formats such
as vector shapefiles, but DXF and DWG can also be read directly
by most GIS software. These CAD data types provide a key bridge
between GIS and engineering applications. For example the LiDAR-derived
elevation contours in the SDW are provided in
both vector shapefile and vector DWG format. Though CAD formats
provide accurate and detailed location information they do not store
attribute information in the same way as GIS vector data does but
rather provide more limited descriptive information in the LAYER
and other DWG entity values.
 Tabular
databases Microsoft Access, SQL Server, Oracle and other relational
database systems serve as storage and access software for a wide
range of tabular data tables. ASCII data is often moved to a tabular
database arranged in a logical integrated manner that emphasizes
relationships between the data sets. As mentioned above, vector
data also incorporates this functionality in storing the data as
attributes, but large complex business tables such as financial
records, census data, etc., are stored and managed as tables in
these more efficient databases. This allows the data to be served
up from a central point to a variety of web-based applications and
query and reporting applications. GIS data, particularly vector
data, can also access these databases through connections within
the GIS software establishing a relationship between the spatial
location of features and the descriptive information about them.
Extracts of information from these relational databases is sometimes
stored in standalone dbase-format (dbf) tables that are highly compatible
with shapefile format data and can be joined to the shapefile dbf
attribute table. As we move to fully integrate spatial data and
attribute data into seamless datasets these standalone tables will
become less common.
GeoDatabase
This close association between spatial vector data and relational
database tables is taken toward a single common format in this next
generation of data storage. As primarily a new data storage mechanism,
not really a new data type, GIS data users will still recognize
data they access through a geodatabase in the common forms discussed
above. Beyond enhanced storage efficiencies and improvements in
access speeds, geodatabases will help integrate the spatial data
of organizations with their extensive business table data. Users
will move from accessing their common data types in a file-based
model as now done to a design where all GIS data location and
attribute is accessed from a relational database. |
