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Fundamentals of GIS data
Users work with geographic data in two fundamental ways:
- As datasets, which are homogeneous collections of features, rasters, or attributes—such as parcels, wells, buildings, orthophoto imagery, and raster-based digital elevation models (DEMs)
- As individual elements—such as individual features, rasters, and attribute values—contained within each dataset
In a GIS, homogeneous collections of geographic objects are organized into datasets about common subjects, such as parcels, wells, roads, buildings, orthophoto imagery, and raster-based digital elevation models (DEMs).
Users work with GIS datasets
Geographic datasets are the primary object collections that users work with in a GIS. They also represent the most common method for data sharing among GIS users.
Datasets are used as the basis for most GIS operations, and provide the primary data sources for:
Datasets provide the key inputs for mapping and visualization
- Globes and 3D scenes
- Geoprocessing inputs and derived datasets
- Data sharing with other users
. Each layer in a map references a dataset and specifies how it will be drawn and labeled.
The map display above was created by drawing numerous datasets—feature classes of cities, country boundaries, rivers, and water bodies—on top of a raster dataset of shaded relief.
Datasets are also used as sources for layers in ArcGlobe and ArcScene views.
Datasets are the primary inputs and outputs for geoprocessing
. ArcGIS includes a rich set of geoprocessing tools. Each tool takes datasets as inputs, performs a transformation on these datasets, and creates results—called derived datasets. A sequence of operations can be assembled into a process
to automate workflows, do analysis, and to automate many critical GIS tasks—hence the term geoprocessing.
Datasets are the primary means for data sharing
. GIS users primarily share their information as individual datasets. Datasets typically come in any number of formats: CAD files, image files, tables, shapefiles, GML files, and so on. A key goal of ArcGIS is for users to work with all the commonly external file formats as well as ESRI supported formats, such as the geodatabase.
Datasets can be listed in ArcCatalog and can be copied and distributed to other GIS users:
ArcGIS supports datasets in its native geodatabase as well as multiple GIS file formats
. ArcGIS works with geographic datasets that are managed in geodatabases as well as in numerous GIS file formats. Geodatabase datasets represent the native data structure for ArcGIS and are the primary data format used for editing and data management.
Users work with individual data elements held in each dataset
In addition to working with datasets, users also work with the individual elements contained in datasets. These elements include individual features, rows and columns in attribute tables, and individual cells in raster datasets. For example:
When you identify a parcel by pointing at it, you're working with the individual data elements in a dataset:
You work with individual data elements when you edit features, a road centerline in this case:
In tables, users work with descriptive information contained in rows and columns.