overview dennis l. johnson what is gis? geographic information system geographic implies of or...

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!