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Overview
Dennis L. Johnson
What is GIS?
• Geographic Information System• Geographic implies of or pertaining to the
surface of the earth• Information implies knowledge of or
collection of some form of data• and finally, a system implies some form of
organization, arrangement, etc.. Perhaps a framework?
GIS Components
• Overview Components:– Data
– Maps/Views/Layouts
– Spatial Analysis
• Physical Components– software
– hardware
– data
– users
– need/application
GIS Software
• Many types• Around for > 30 years• Only really prevalent for ~20 yrs?• We will be using ArcView by ESRI• Also ArcInfo by ESRI• GIS software is loosely defined• Some more applicable to certain tasks - ERDAS
for example.
Hardware
• Software may dictate hardware in some cases
• Generally:
• computer
• database
• printers and plotters, etc....
Data
• From many sources
• field collected
• spatial in nature
• point, line, polygons, grids
• METADATA!!!!!!!
Users
• Very wide range
• some users, some doers, etc...
• some want pictures
• some want answers
• some want to do analysis
• know your audience!
• know your needs!
Applications
• What is the desired final product?
• Will the tasks be repeated over and over?
• Or is this a one time application?
What does a GIS do?
• Input data
• Manage data
• Manipulate data
• Perform analyses
• Produce output - maps, charts, a single number?
Let’s jump right to Arcview
• Organizes your data into a PROJECT
• A PROJECT contains:
• views, tables, charts, layouts, and scripts.
• Each of the above components also contains so-called components.
• Notice that I did not mention DATA!!!!!
Views
• Display themes or geographic data
• A view has an area for displaying the theme and an area for the “table of contents” - or what views are presently loaded.
Tables
• Display tabular data or the descriptive attributes of the elements in the data set.
Charts
• Display data graphically
• Different than the map type displays
Layouts
• The whole shebang?!?!?!
• Put it all together
Scripts
• Small computer programs
• Allow repeatability.....
• AVENUE
• Extensions
Database Structures
Database Structures
• The database structures allow very powerful relationships:
• one-to-one - site one is a corn field - one site --> one land use..
• One-to-many - Many sites are corn fields.... Corn fields are code #1 and in another file - code #1 is corn field!
• Many-to-many - a site may have several research quadrates, which in turn has many point sampling sites, which in turn has multiple species.....!!!!
Relational Database Management Systems
• Use ROWS or RECORDS
• and PRIMARY KEYS
• Let’s look at an example.....
A relational database...Quadrat # Collector Date Site no.
1 Smith 6/10/96 22 Jones 7/1/96 53 Johnson 8/5/97 1
Quadrat # Species # Lat Long.1 3 35.19 72.401 4 35.18 72.362 2 35.21 72.51
Species # Name Type1 Conomyrma insana Generalist2 Pogomomyrmex rugosusSpecialist3
Basic Data Structures
• Points
• Lines
• Polylines
• Polygons
• Raster Data
Points
• A single X,Y coordinate pair...
• Location in space is provided...
• May now be attributed
• What types of data may be best represented by a point?
Point #1 - X,Y
Lines
• Connected Points• Multiple X,Y coordinate pairs.• 2 points make up a line• What do 3 points make up?• What types of attributes can you add to a line?• A collection of lines in a complex form may be
called a NETWORK.• What is best represented with a LINE?
Polygons
• What differentiates a polygon from a line?
• What type of attributes can we think of for a polygon?
• What is best represented by a polygon?
Raster Data Structures
• A gridded approach.
• Each grid cell is a constant value
• Grid cells are generally a constant size or shape
Raster, cont...
• What are some advantages?
• Disadvantages?
• What might we represent with RASTER structures?
• How might you convert a point, line, polygon to raster?
FEATURES
These points, lines, polygons are called features....
We will leave raster data alone for a while..
Feature Representation
• We represent the features in space with coordinates....
• We may attribute them.
• In order to define relationships (spatially) - or between and among themselves...
• We must provide topology.
Topology
• Best illustrated rather than stated...
Nodes: from node and to node - what does this imply?
Topological Model
Using FROM NODES and TO NODES, I can assign direction and left and right attributes - this requires and additional file!
Topological models are essential for some of the advanced GIS tasks..
1
2
ArcView
• Shapefiles - the native file structure
• Non-topological!
• Are used to store geometric and attribute information
Shapefiles - multiple files
• .shp - feature geometry
• .shx - index of the geometry
• .dbf - dBASE file for attributes
• may also see:
• .sbn, .sbx, .fbn, .fbx, ain, .aih
• and : .prj
• and : .xml
What’s a Project?P ro jec t C om p on e n ts
V ie w sV ie w 1V ie w 2
T a b lesT a b le 1T a b le 2
C h a rtsC h a rt 1C h a rt 2
L a yo u tL ayo u t 1L ayo u t 2
P ro je ctX X X X X .a pr
Project may contain several types of “documents”
A Project is also a file - .apr
3 Main Parts of a Project
• Documents - provide different means of visualizing and interacting with your data: views, tables, layouts, script editors, and charts.
• GUI’s - Document User Interfaces (DocGUIs) define the controls used to interact with the documents. DocGUIs may be system defined or local to the project.
• Scripts - are written in Avenue and perform various tasks in ArcView.
The parts of a project are actually “objects” or often “classes”
How many have heard of Object Oriented Programming?
!Note!
I did not say that a project contains DATA!
In fact... A project file refers to data
Path: c:/temp/quinter/gravidfemales.shp
The files are in a directory
That directory is generally called:
The WORKSPACE
Recap the PROJECT
• The project (a file) contains information about the “documents” (tables, charts, views, etc..) that are associated with the project.
• It does not contain data!• Rather it refers to the data in the WORKSPACE.• The default WORKSPACE is often the “temp”.
Points to be made
• If you DELETE the project - you do not delete the data.
• If you DELETE the data the project is still there (in theory) but not in reality! WHY?
This is what happens
The project file was looking for a theme called “hlshd7”
A Common Pitfall
• You work and create a theme or 2 and SAVE the project. Everything looks fine.
• You even shut down ArcView and start it back up again at the same computer and it works fine.
• Later that week - you are working on the project and you fire up ArcView and:
Ughhh - the sequence begins...
“Dr. Johnson - I did everything you said and this is the message I got....”
I know he never told me aboutthat workspace thing!