GIS Exam 1

Feature Types

- In a GIS there are two types of features: discrete features and continuous features 1) discrete features - associated with a specific geographic location - points, lines and polygons are all considered to be discrete features --points (e.g. cities on a world map, oil wells, landmarks, etc) --lines (e.g. streams, roads, pipelines, elevation contours, etc) --polygons (e.g. counties, parks, soils, land parcels) 2) continuous features - have no defined location - they can be measured anywhere on a map - can be mapped as a surface (e.g. temperature, elevation, precipitation) - note that surfaces often start out as a series of sample points (regularly or irregularly spaced) - to calculate a surface, GIS interpolates the surface values between the points

How does a GIS work?

- a GIS operates on the premise that all of the features in the real world can be represented by: --points (e.g. wells, landmarks, cities on a world map) --lines (e.g. roads, rivers, pipelines, transmission lines) --polygons (e.g. soils, vegetation types, land-use parcels, counties, states) --surfaces (e.g. elevation, temperature, barometric pressure) ---note: how features are represented (as points, lines or polygons) depends upon the scale of the map ---also note that digital airborne or satellite imagery can be added in ArcMap to help visualize features - these point, line, polygon and surface features are organized into logical layers (e.g. a roads layer, a soils layer) - and these layers (each representing a particular feature type) can be overlaid to map spatial relationships - this overlay process is the essence of digital cartography - but a GIS is much more... - in a GIS the point, line and polygon layers are associated with an attribute table - and each feature represented in a map layer is dynamically linked to a record in the attribute table - or, conversely, each record in the attribute table is dynamically linked to a feature on the map - in other words, a GIS links features in the real world to information about those features - this relationship between map features and records in an attribute table is extremely important - it allows us to query and analyze data based upon location (which cannot be done in a standard database)

Basic Characteristics of Maps

- all maps are concerned with location --location of features defined by points, lines, polygons - or surface values - all maps are scaled reductions of reality --the map scale defines the relationship between the map and reality - all maps involve some abstraction of reality --can't show every feature in the real world - only selected layers are displayed --level of abstraction depends upon: 1) the purpose of the map and 2) the map scale - all maps involve some generalization of reality --features are simplified (e.g. cities are represented by points, roads are represented by simple lines) --level of generalization depends upon: 1) the purpose of the map and 2) the map scale - all maps use symbology to represent features --features are symbolized by varying size, colors, tones, patterns, or using specialized symbols - all maps involve transformations of reality -- map projections are used to represent a spherical surface of the Earth on a flat map

Qualitative thematic maps

- categories of non-numerical data (e.g. soils, vegetation, land use) - features are distinguished by a name, text or descriptive information (eg soil name) and a symbol is assigned to each feature or class of features

What is a GIS map?

- dynamic maps that can zoom in or out to see different areas with more or less detail - can access a variety of layers and determine how features in each layer are displayed and symbolized - provides access to a database of information about features through attribute tables - permits edit, query and analysis of map data - abstraction: only selected features (layers) are displayed, can't show every feature in the real world - generalization: features are simplified, can't show all of the detail associated with real-world features

ARC/INFO

- prior to the summer of 2001 ESRI had two main software products --ARC/INFO - a professional GIS originally developed in the 1970's ---a command-line software package - very powerful but difficult to use

For General Mapping Purposes

- the vector data model to represent discrete points, lines and polygons - and the raster data model to represent continuous surfaces

ArcCatalog

-ArcCatalog is a completely separate application used to browse, manage and document geographic data - Supports metadata or 'data about the data' which describes or documents a geographic data (e.g. date created, description of features, who created it, etc.).

Qualitative Thematic Maps

-Developed based upon the classification of descriptive (categorical, nominal) data

Quantitative Thematic Maps

-Developed based upon the classification of quantitative (numerical) data1) Counts: map the total number associated with a feature - counties mapped by total population (polygon example) - businesses mapped by number of employees (point example) 2) Amounts: map the total dollar value or magnitude associated with each feature - gross tax revenue by county (polygons) - per student school expenditure (points) - earthquake magnitudes (points) 3) Ratios: map the relationship between two variables (normalize) - ratios even out the inherent difference between large and small areas - e.g. the size of a country, state or county becomes irrelevant when mapping ratios - most common ratios are averages, proportions, and densities a) averages - divide quantities that use different measures - people per household = population / number of households b) proportions (percentages) - divide quantities that use the same measure - percent senior citizens = population over 65 / population c) densities - divide a quantity by the area of the feature - population per square mile = population / square mile

ArcToolBox

-Provides an organized collection tools that can be used for GIS analysis, data management, data conversion and other tasks. - Can be accessed within the Catalog window, ArCatalog or from the ArcToolbox window.

Types of Qualitative Data

-Qualitative data can be a names, types, or ranks 1) Names: (unique values) different colors used to symbolize unique names (ex. map of states, counties or water bodies) 2) Types: (different categories) features are grouped by type and mapped (ex. map of different stores or land use zones) 3) Ranks: features are ranked from low to high (for example, from 1 - 5 but represents relative values and not strictly numeric intervals. Values also can be descriptive) - rankings show relative values (poor, fair, good, excellent - or - low, medium, high) - used when it is difficult to quantify an attribute - relative value of scenic streams (low scenic value = 1, high scenic value = 5) - soil types used for growing a particular crop (poor soils = 1, good soils = 5) - used when a range of values is adequate for a particular purpose - permeability of soils for a septic system (clay soils = 1, sandy soils = 5)

Catalog Window

-The Catalog window provides a subset of functionality of the full ArcCatalog application - is available in the ArcMap application and is used to browse and manage data - Provides ability to connect to folders to access geographic data

Types of Quantitative thematic maps

-There are many different ways in which quantitative data can be mapped --graduated color map (choropleth map - colored or shaded polygons) --graduated symbol map (symbol size varies based upon the number of classes) --proportional symbol map (symbols sized varies proportionally to feature attribute values) --dot density map (number of dots in an area represents a count (e.g. 1 dot = 500 dairy cows) --pie chart / bar chart / stacked chart maps (useful for mapping more than one variable) --isoline maps - used to map surfaces, vector lines derived from rasters (e.g. contours, isobars, isotherms) --colored or shaded rasters - used to map surfaces (color or shades vary with grid cell values)

Quantitative thematic maps

-classification of numerical data (e.g. bank assets, pop density) - features are distinguished by numbers (eg population)

What is GIS?

-definition: A geographic information system is a computer system* designed to manage and analyze spatial data, where spatial data can be any data that are tied to places or geographic coordinates. *the five components of a computer system include: --1) hardware, 2) software, 3) data, 4) people, and 5) work flow procedures -to manage and analyze spatial data, a GIS has six major functions. --GIS software provides users with the ability to: 1) capture, 2) store, 3) manipulate, 4) query, --5) analyze and 6) display spatial data (know these six main functions).

Map Scale

-given that a map is a scale model of the surface of the earth ... - the map scale tells a map reader the scale at which the earth's surface is being represented - there are three main types of map scale (know the advantages and disadvantages of using each type) 1) verbal scale: easy to understand difficult to convert units not valid if map is enlarged or reduced 2) bar scale: easy to understand remains valid if map is enlarged or reduced difficult to convert units 3) representative fraction (ratio): not dependent on measurement units difficult to visualize not valid if map is enlarged or reduced - to overcome the limitations associated with a single type of map scale, the USGS uses four different types of map scales on a standard topographic map. These four map scales are: 1) the representative fraction, 2) a bar scale in miles, 3) a bar scale in feet and 4) a bar scale in kilometers Important: As with any scale, you should trust its accuracy only in the center of the map. The map scale is only as an approximation of distances around the edges, especially for map that depict large areas.

ArcGIS

-in the summer 2001 - ESRI introduced ArcGIS (a suite of GIS software programs) --ArcGIS consists of two application programs: ArcMap and ArcCatalog --ArcMap is used for data analysis and to create map products- ArcCatalog is used for file management - ArcGIS can be licensed at three levels with increasing functionality - the three license levels of ArcGIS 10 are called Basic, Standard, and Advanced - as you move from Basic to Standard to Advanced, the software includes more tools (functionality) - main advantage: user interface is the same across the Basic, Standard, and Advanced versions - there are also dozens of extensions available for core ArcGIS software - some of the extensions are licensed and some are free - some common extensions include: Spatial Analyst, Network Analyst, 3D Analyst, etc - these extensions add specialized tools (functionality) to the core software

Esri Software History

-in this class we will use GIS software products developed by Esri --original name: Environmental Systems Research Institute --then the company became known as ESRI and now the name is simply Esri --Esri is a privately owned software company owned by Jack and Laura Dangermond --headquarters located in Redlands, California - regional offices throughout the U.S. and the world

Types of Maps

-maps are categorized by their 1) scale and 2) function (e.g. a small scale, quantitative or qualitative thematic map) 1) Maps Categorized by Scale - we often use the terms "large scale" and "small scale" to describe maps - these are relative terms on a continuum of scales (some examples below) 1:10,000,000 1:1,000,000 1:250,000 1:24,000 1:5000 very small scale small scale medium scale large scale very large scale - a country - a state - county - topo map - a neighborhood - do not be confused on this... - for example, a world map is a very small scale maps (even though it covers the whole world) --this is because the fraction 1/10,000,000 is a much smaller number (fraction) than 1/5,000 --an easy way to remember is: - large scale maps have large features - small scale maps have small features - comparing large scale vs small scale maps, be familiar with the following properties: Large Scale (1:5,000) Small Scale (1:1,000,000) --area covered small area large area --level of abstraction less abstract more abstract --level of generalization less generalized more generalized --projection* less important more important --errors associated w/ datum+more important less import *Takes into account curvature of the earth and affects size and shape of countries +A reference point for coordinate systems 2) Maps Categorized by Function - general reference maps --road maps, topographic maps, atlases, etc. --can fulfill many purposes - cadastral maps or plat maps - used by cities, planners and developers to represent lots and various areas in a city --property boundaries (polygons) - derived from a cadastral survey - charts - Navigation maps are generally referred to as a chart --maps used for navigation (nautical or aeronautical charts)

Thematic Maps- two types

-qualitative and quantitative - single purpose maps based on a particular theme or layer - map usually focuses on a particular layer that is symbolized on one attribute - can communicate more specific information about certain features than a general reference map that is intended to show feature locations.

What is a map?

-simple definition: a map is a scale model of the part or all of the surface of the earth -like all scale models, a map is an abstracted and generalized version of reality

Origins of GIS

-the Canadian Geographic Information System (CGIS) was the first operational GIS --developed in the early 1960's, the era of mainframe computers --the system was designed to inventory land use and assist in the management of natural resources --Roger Tomlinson is considered the "father of GIS" for his role in the development of the CGIS

Advantages and disadvantages of the vector and raster data models

1) vector data model - advantages of the vector model --smaller data sets (file sizes) --computationally efficient --greater precision --map features are tied to an attribute table - disadvantages of the vector model --difficult to handle continuous surfaces (surfaces must be represented by isolines or polygons) 2) raster data model - advantages of the raster model --ideal for mapping continuous data (elevations, temperatures, etc) --ideal for use with digital remote sensing data (digital imagery is a raster data set) - disadvantages of the raster model --large data sets (file sizes) --not computationally efficient --less precision --features are not tied to an attribute table (see notes below)* *continuous rasters - a continuous raster is used to represent and display surfaces - in this case, the grid cell values are decimals that represent a measurement or estimate --e.g. each grid cell has a unique temperature or elevation value - because each grid cell can have a unique decimal value, and there can be millions or grid cells in a raster dataset, it is not practical to link each grid cell to a record in an attribute table --e.g. it is not practical to have an attribute table with millions of records - in a continuous raster, there is no attribute table *discrete rasters - a discrete rasters is used to represent points, lines and polygons - in this case, the grid cells values are integers that represent feature class codes --e.g. vegetation class codes, land use class codes, or river class code - a discrete raster layer has a value attribute table - a value attribute table only shows the number of grid cells associated with each feature class code

ArcView

ArcView - a desktop GIS developed in the 1990's --original version was developed as a viewer (for data analyzed in ARC/INFO) --throughout the 1990's ArcView evolved into a fairly powerful desktop GIS --the software was easy to use and had a nice graphical user interface

Lines

Discrete, 2 or more connected x, y coord pairs, connected grid cells (integer feature class codes)

Polygons

Discrete, 3 or more connected x, y coord pairs that close to form a polygon, contiguous group of grid cells (integer feature class codes)

Points

Discrete, x,y coordinate pair, single grid cell (integer feature class codes)

Geospatial Technology

Geospatial technology is a collective term used to describe the integrated use of geographic information systems,remote sensing, global navigation satellite systems, digital cartography and Internet mapping.

ArcMap

In ArcMap the layers displayed in the Table of Contents (TOC) are used to view, symbolize and analyze geographic information. - The layers are only a representation of the data within a map document. - The layers reference the data using a path name to the data which are stored on disk

Surfaces

continuous, represented by isolines or polygons, usually decimal grid-cell values but can also be integer feature class codes ex. representing land use types

Data Models

to represent features, there are two data models: the vector data model and raster data model 1) vector data model - feature representation: --discrete points (x,y coordinate pair)- discrete lines (two or more connected x,y coordinate pairs) - discrete polygons (three or more x,y coordinate pairs connected to form a polygon) - continuous surfaces (must be represented by isolines or polygons) 2) raster data model - feature representation: --discrete points (single grid cell with integer cell values to represent feature class codes) --discrete lines (connected grid cells with integer values to represent feature class codes) --discrete polygons (contiguous group of grid cells with integer values to represent FCCs) --continuous surfaces (grid cells are measurement or estimate decimal values)