GIS Basics

Terms & Concepts Important for GIS

Dori Dick, dickd@geo.oregonstate.edu

http://www.marinegis.org/whatIsGIS.html

What is GIS?

Geographic Information System

Collection, organization, maintenance, analysis and output of spatial data

2 important components

Where?

coordinates

What?

attributes

http://www.townofbernalillo.org/depts/gis.htm

2 Major Classes of Spatial Data

Vector

- Defines real world features using object data model

- Points, lines, polygons

- Shapefiles, feature classes

- Discrete data & attributes

(in a table)

Raster

- Defines real world features using field data model

- Grid of equal-sized cells

- Grids, satellite data, jpgs

- Discrete & continuous data

Marine Vector Data

Points

- A set of x,y coordinates

e.g. Animal or sample locations

Lines

- A series of connected x,y values

e.g. ship track, shoreline

Polygons

- Areas bounded by lines

e.g. MPAs, oil spill

http://sanctuaries.noaa.gov/science/condition/gfnms/images/fig46_lg.jpg

From Nur et al. 2011

Marine Raster Data

Surfaces

- Each cell has one and only one value

- Spatial resolution (cell size) ranges from 1 km, 4km, 9km, and even bigger

e.g. bathymetry, SST, chlorophyll concentration

Spatial Reference System

Provides a way to assign coordinates

to a location and establish a

relationship between coordinates to

represent a position in real world space

Consists of:

Datum refers to the shape of the earth e.g. World Geodetic System (WGS) 1984, North American Datum (NAD) 1983

Coordinate System

i. Spherical/ Geographic units in degrees e.g. Latitude/Longitude

ii.Rectangular/Projected -- linear units e.g. meters, miles, fathoms

Projection conversion of locations from 3D to 2D surface e.g. Universal Transverse Mercator (UTM), Albers

Spatial Reference Contd:

The default setting on most

handheld GPS units is WGS84

and no projection

Data are collected in degrees

In ArcGIS x,y coordinates must be in decimal degrees

e.g. using Degrees + Minutes/60 + Seconds/3600

34N 22 65 = 34.384722

** Lat and/or Long must have a negative sign if in

Southern or Western hemisphere **

https://weblogs.java.net/blog/manningpubs/archive/2013/02/13/spatial-reference-system-what-it

GIS Terms

Feature Classes used to represent vector data

1. Shapefiles

Comprised of several files - .shp, .shx, .dbf

PLUS .prj, .sbn, .sbx etc.

Unable to support date time formats well

2. Geodatabase Feature Classes

Supports date time

Contained within a Geodatabase

File Geodatabase

A file folder that holds a collection of GIS datasets

Raster A grid file

Line

Polygon

Point

GIS Terms

ArcCatalog ArcGISs file explorer & data manager

ArcMap Desktop application for map based tasks, creates an .mxd file

ArcToolbox -- Complete, comprehensive set of tools for geo-processing, data conversion, map management, overlay analysis, map projection, and much more

geneGIS Toolbar --

ArcMap

Main Menu

Standard Toolbar

Basic Tools

Table of Contents

ArcMap

Add data ArcCatalog

ArcToolBox

Pan

Zoom to Full Extent

Select

Elements Identify

Connecting to a Folder

Use

Connect To Folder

Button

Navigate to the folder where

your GIS data are located

DO NOT click into the folder

itself!

GIS Tips

Do not use spaces when naming files, instead use an underscore ( _ ) e.g. whale_species

Use Arc Catalog NOT Windows Explorer when managing, moving, renaming GIS data

Use the ArcGIS Help menu, Google (indicate ArcGIS 10.1)

ArcMap is a data viewer it does not store your data, so if you transfer your data to another computer and open your .mxd file, you will need to tell the computer where to find your GIS files repair the data source

Available GIS Resources

Esri Support

http://support.esri.com/en/

ArcGIS Resources

http://resources.arcgis.com/en/help/main/10.1/index.html#/ArcGIS_tuto

rials/00qn0000013t000000/

Esri Virtual Campus

- Web-based, short courses, many are free

http://www.esri.com/training/main

ArcGIS 10.1 Help

- Directly from within ArcGIS 10.1

- Online at http://resources.arcgis.com/en/help/main/10.1/index.html#//00v200000005000000