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Overview

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

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Overview

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  1. Overview Dennis L. Johnson

  2. 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?

  3. GIS Components • Overview Components: • Data • Maps/Views/Layouts • Spatial Analysis • Physical Components • software • hardware • data • users • need/application

  4. 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.

  5. Hardware • Software may dictate hardware in some cases • Generally: • computer • database • printers and plotters, etc....

  6. Data • From many sources • field collected • spatial in nature • point, line, polygons, grids • METADATA!!!!!!!

  7. 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!

  8. Applications • What is the desired final product? • Will the tasks be repeated over and over? • Or is this a one time application?

  9. What does a GIS do? • Input data • Manage data • Manipulate data • Perform analyses • Produce output - maps, charts, a single number?

  10. 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!!!!!

  11. 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.

  12. Tables • Display tabular data or the descriptive attributes of the elements in the data set.

  13. Charts • Display data graphically • Different than the map type displays

  14. Layouts • The whole shebang?!?!?! • Put it all together

  15. Scripts • Small computer programs • Allow repeatability..... • AVENUE • Extensions

  16. Database Structures

  17. 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.....!!!!

  18. Relational Database Management Systems • Use ROWS or RECORDS • and PRIMARY KEYS • Let’s look at an example.....

  19. A relational database...

  20. Basic Data Structures • Points • Lines • Polylines • Polygons • Raster Data

  21. 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

  22. 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?

  23. 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?

  24. Raster Data Structures • A gridded approach. • Each grid cell is a constant value • Grid cells are generally a constant size or shape

  25. Raster, cont... • What are some advantages? • Disadvantages? • What might we represent with RASTER structures? • How might you convert a point, line, polygon to raster?

  26. FEATURES These points, lines, polygons are called features.... We will leave raster data alone for a while..

  27. 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.

  28. Topology • Best illustrated rather than stated... Nodes: from node and to node - what does this imply?

  29. 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

  30. ArcView • Shapefiles - the native file structure • Non-topological! • Are used to store geometric and attribute information

  31. 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

  32. What’s a Project? Project may contain several types of “documents”

  33. A Project is also a file - .apr

  34. 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.

  35. The parts of a project are actually “objects” or often “classes” How many have heard of Object Oriented Programming?

  36. !Note! I did not say that a project contains DATA!

  37. In fact... A project file refers to data Path: c:/temp/quinter/gravidfemales.shp

  38. The files are in a directory

  39. That directory is generally called: The WORKSPACE

  40. 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”.

  41. 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?

  42. This is what happens The project file was looking for a theme called “hlshd7”

  43. 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:

  44. “Dr. Johnson - I did everything you said and this is the message I got....” I know he never told me about that workspace thing! Ughhh - the sequence begins...

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