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"What is" Links
What is a geodatabase?
At its most basic level, the geodatabase is a container for storing spatial and attribute data and the relationships that exist among them. In a geodatabase, which is a vector data format, features and their associated attributes can be structured to work together as an integrated system using rules, relationships, and topological associations. In other words, the geodatabase allows you to model the real world as simply or complexly as your needs dictate. Geodatabases are created, edited, and managed using the standard menus and tools in ArcCatalog™ and ArcMap™. Source: GIS.com
What is a data model?
Data models are the rules the GIS follows, such as "county lines do not overlap," and are essential for defining what is in the GIS as well as supporting the use of GIS software. All spatial data models fall into two basic categories:
Vector data model. Discrete features, such as customer locations and data summarized by area, are usually represented using the vector model.
- The vector data model represents each feature as a row in a table, and feature shapes are defined by x,y locations in space (the GIS connects the dots to draw lines and outlines). Features can be discrete locations or events, lines, or polygons.
- Locations such as the address of a customer or the spot a crime was committed are represented as points having a pair of geographic coordinates. Lines, such as streams or roads, are represented as a series of coordinate pairs. Polygons are defined by borders and are represented by closed polygons. They can be legally defined, such as a parcel of land; administrative, such as counties; or naturally occurring boundaries, such as watersheds.
When you analyze vector data, much of your analysis involves working with (summarizing) the attributes in the layer's data table.
Raster data model. Continuous numeric values, such as elevation, and continuous categories, such as vegetation types, are represented using the raster model.
- The raster data model represents features as a matrix of cells in continuous space. Each layer represents one attribute (although other attributes can be attached to a cell). Most analysis occurs by combining the layers to create new layers with new cell values.
- The cell size you use for a raster layer will affect the results of the analysis and how the map looks. The cell size should be based on the original map scale and the minimum mapping unit. Using too large a cell size will cause some information to be lost. Using a cell size that is too small requires a lot of storage space and takes longer to process without adding additional precision to the map. Source: GIS.com
What is data?
Geography is information about the earth's surface and the objects found on it. This data comes in three basic forms:
Map data. Map data contains the location and shape of geographic features. Maps use three basic shapes to present real-world features: points, lines, and areas (called polygons).
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Map data includes points, lines, and polygons.
- Points represent anything that can be described as an x, y location on the face of the earth, such as shopping centers, customers, utility poles, hospitals, or cellular towers.
- Lines represent anything having a length, such as streets, highways, and rivers.
- Polygons describe anything having boundaries, whether natural, political or administrative, such as the boundaries of countries, states, cities, census tracts, postal zones, and market areas.
Map data is defined according to one of two models used to represent data in a GIS. It is called a vector model . With a vector model, each feature is defined by x, y locations in space (the GIS connects the dots to draw lines and outlines, creating lines and polygons).
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Another model is the raster model . With the raster model, features are represented as a matrix of cells in continuous space. A point is one cell, a line is a continuous row of cells, and an area is represented as continuous touching cells.
Attribute data. Attribute (tabular) data is the descriptive data that GIS links to map features. Attribute data is collected and compiled for specific areas like states, census tracts, cities, and so on and often comes packaged with map data. When implementing a GIS, the most common sources of attribute data are your own organization's databases combined with data sets you buy or acquire from other sources to fill in gaps.
Image data. Image data ranges from satellite images and aerial photographs to scanned maps (maps that have been converted from printed to digital format).
- Images can be displayed as maps along with other spatial data containing map features. Image data offers a quick way to get spatial data for a large area and is more cost- and time-effective than trying to collect layers of data like buildings, roads, lakes, etc,. one at a time. However, image data is one file, or layer, so you can not break down the different components and attach data to them separately. Image data is the best choice if you need to add a point of reference to vector data without attaching additional information.
- Images can also be attributes of map features. In other words, you can add images to other map features so that clicking on the feature would display the image. For example, you might have a map of California with cities. By clicking on the point that is the City of San Francisco, you open up an image of San Francisco.
Almost any document or photograph can be scanned and stored as an attribute in a GIS database. Photos of houses for sale can be linked to a real estate map, field data forms can be linked to sample sites, and scanned permits can be linked to building sites. Source: GIS.com
What is Geoprocessing