Introduction to ArcGIS

1
Introduction to ArcGIS
2

• How data are stored in ArcGIS
• Components of ArcGIS ArcMap, ArcCatalog and
  ArcToolbox
• Extensions of ArcGIS spatial analyst,
  geostatistical analyst and 3D analyst

3
Often-Used Applications

• ArcCatalogused to browse and manage geographic
  data sources and create and update metadata
• ArcMapused to display and query geographic data
  on maps and to edit and output data
• ArcToolboxcontains powerful tools for performing
  geographic analysis and data conversion

4
Arc Catalog
Graphical previews
View data (like Windows Explorer)
Tables
Metadata
Somenahalli, Sekhar, University of South Australia
5
Arc Map
View and edit data
Analyze data (Geoprocessing)
Create maps
Somenahalli, Sekhar, University of South Australia
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Somenahalli, Sekhar, University of South Australia
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Arc Toolbox
Somenahalli, Sekhar, University of South Australia
8
Geographic Data

• Concepts
• File Formats
• Topology

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Geographic Data Classic Approach

• Two components of geographic data
• Spatial Data representations of geographic
  features associated with real-world locations
• Stored in files and managed by the GIS software
• Attribute Data descriptive information
• stored in tables and managed by an RDBMS
  (relational database management system)
• Two formats for geographic data
• Raster data rectangular array of cells or pixel
• Vector data three feature types
• points/nodes (single x,y locations)
• lines/arcs (linear string of x,y locations)
• areas/polygons (closed string of x,y locations)

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Geographic Data Object-Oriented View

• Object View
• The real world is a series of entities located in
  space.
• An object is a digital representation of an
  entity, with three types
• Point objects
• Line objects
• Area objects
• The same entity can be represented at different
  scales by different object types the
  multi-representation problem
• Behavior can be associated with objects thus they
  can change over time
• Field View
• The real world has properties which vary
  continuously over space every place has a value
• May be represented as raster data, or with
  vector data as a TIN (triangulated irregular
  network
• If the value is a categorical or integer
  variable, then places with the same value (e.g.
  soil type) can be grouped--and doesnt this give
  us an area object?!

11
File Formats for Vector Spatial Data

• Coverage vector data format introduced with
  ArcInfo in 1981
• multiple physical files (12 or so) in a folder
• proprietary no published specs ArcInfo
  required for changes
• Can be exported to a single E00 (E-zero-zero)
  file for transfer
• Shape file vector data format introduced with
  ArcView in 1993
• comprises several (at least 3) physical disk
  files (with extension of .shp, .shx, .dbf), all
  of which must be present
• openly published specs so other vendors can
  create shape files
• Geodatabase new format introduced with ArcGIS
  8.0 in 2000
• Multiple layers saved in a singe .mdb (MS
  Access-like) file
• Proprietary, next generation spatial data file
  format

Shapefiles are the simplest and most commonly
used format.
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Anatomy of Spatial File Formats

• Shapefile
• Geodatabase
• Coverage

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Spatial File Formatsexample ArcCatalog View
Tracts feature class table (attributes in
columns)
Features (rows)
Feature type
Feature ID (key field)
Secondary or Foreign key
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Spatial File Formats NT Explorer View
Info master folder for AVCAT workspace
Tracts coverage
Trans coverage
Locator (table)
Personal Geodatabase
Raster
Tracts shapefile
Trans shapefile
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Shapefiles

• Openly published structure for spatial data
  (Coverages Geodatabases are proprietary)
• Partially an attempt (successfully!) by ESRI to
  make their format the industry standard
• Much simpler than coverages rather than multiple
  folders and files, three main files with same
  name (road) but different extensions, e.g.
• road.shp road.shx road.dbf
• Attribute (feature) data stored in dBase (.dbf)
  file
• Can be edited in Excel (or other) but do not
  change the number of rows
• If you add columns, may need to change refers
  to definition via Insert/Name/Define
• Files can be dragged, dropped, cut and pasted
  into other folders -- providing the complete file
  set is moved.

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Coordinate Systems

• All spatial data is in a coordinate system

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Coordinate Systems

• Coordinate System consists of two main things
• Datum normally NAD 27 or NAD 83
• The same location may have different coordinates
  because of the datum
• Projection
• The transformation by which 3D lat/long is
  converted to 2D X/Y Cartesian values
• Parameters normally required to describe the
  exact nature of the projection
• Projected Coordinates must be in some measurement
  unit usually feet or meters
• A geographic projection uses lat/long values as
  X/Y Cartesian coordinates (not recommended)
• Thus, for any a spatial data set, knowing simply
  the name of the projection is not sufficient.
  Must also know
• Datum
• Parameter(s)
• Measurement units

18
Define versus Project

• Define
• Informs the ArcGIS system of the datas actual,
  current projection.
• Is essentially metadata. For shapefiles and
  coverages, saved in a .prj file
• Does not change the actual data.
• Define it wrong, and all subsequent analyses or
  projections of that data are likely to be wrong!
• Project
• Actually projects the data. Think of this as
  reproject.
• The data does change.
• The current projection (input) must already be
  known by the ArcGIS system,
• That is, you have to do a Define first, if
  somebody has not already done it
• The desired projection (output) is specified on
  the Project command.