WILD 3710 Lab 3: GIS Data Exploration Camp W.G. Williams

Transcription

1 WILD 3710 Lab 3: GIS Data Exploration Camp W.G. Williams -Laboratory- TAs and Lab Instructors: Chris McGinty Office: JQL 146 Office Hours: W 2:30 3:30 or by appt. Alex Hernandez alex@gis.usu.edu No Office Hours Lab Overview This goal of this lab is to give you a further understanding of the GIS software and help you grasp the concepts and importance of geospatial data in the context of our study area. This Week -- 1) Theory a) Metadata (What, Why, How) b) c) Scale & Map Scale d) Map Composition & Display Lab Overview This Week -- 1) Application a) To begin our research we would like to explore some Nevada Scrub-Jay (Aphelocoma californica nevadae) nesting data. b) This Week s Question: The manager of our project wishes to determine the number of active Scrub-Jay nest sites within a.5 km buffer of roads on the Camp Williams Utah National Guard Training site. This information will aid in determining the potential vehicle impact on brooding pairs within the buffer. c) Deliverables: We have been asked to provide a brief report explaining the processes and methods we used to determine the number of active nest sites AND a simple map detailing our findings. 1

2 Metadata What is Metadata? Simply put, metadata is information about your data. Modified from Langs-Stoner, 2004 Metadata This is the metadata for this. Emily and Madison What s Missing? Modified from Langs-Stoner, 2004 Metadata This is the metadata for this. Rodale's Rodale's illustrated illustrated encyclopedia encyclopedia of of herbs herbs ISBN: x (pbk.) : $17.95 ISBN: x (pbk.) : $17.95 ISBN: : $24.95 ISBN: : $24.95 Title: Rodale's illustrated encyclopedia of herbs / Title: Rodale's illustrated encyclopedia of herbs / Claire Kowalchik & William H. Hylton, editors ; Claire Kowalchik & William H. Hylton, editors ; writers, Anna Carr... [et al.]. writers, Anna Carr... [et al.]. Publication info: Emmaus, Pa. : Rodale Press, c1987. Publication info: Emmaus, Pa. : Rodale Press, c1987. Physical descrip: vi, 545 p. : ill. (some col.) ; 24 cm. Physical descrip: vi, 545 p. : ill. (some col.) ; 24 cm. General Note: Includes index. General Note: Includes index. Subject term: Herbs. Subject term: Herbs. Subject term: Herbs--Utilization. Subject term: Herbs--Utilization. Subject term: Herb gardening. Subject term: Herb gardening. Subject term: Herbs--History. Subject term: Herbs--History. Subject term: Herbals. Subject term: Herbals. Added author: Kowalchik, Claire. Added author: Kowalchik, Claire. Added author: Hylton, William H. Added author: Hylton, William H. Added author: Carr, Anna, Added author: Carr, Anna, Added author: Rodale Press. Added author: Rodale Press. Modified from Langs-Stoner, 2004 While the card-catalog entry is a form of metadata, it does not address topics such as quality, accuracy, or scale. Well-written geospatial metadata describes these and many more aspects of the data. 2

3 Metadata This is the metadata for this. Modified from Langs-Stoner, 2004 Metadata Properly documented data provides vital information to interested parties. Modified from Langs-Stoner, 2004 Metadata Metadata can describe a variety of data. Data set GIS GIS files files Imagery Imagery Geospatial Geospatial Databases Databases GPS GPS data data Biological Biological data data In In situ situ data data Metadata Title Title Scale Scale Source Source Content Content Location Location Publication Publication Access Access Modified from Langs-Stoner,

4 Metadata Metadata describes Characteristics of the data CONTENT CONDITION QUALITY consistently. Modified from Langs-Stoner, 2004 Think of it as a component of the data. Metadata ArcCatalog can (and should) be used to create, edit, and view metadata associated with shapefiles, raster datasets, and ArcInfo coverages. Note the Metadata Tab Metadata By clicking the Metadata tab, we are directed to the metadata sheet. This sheet has three sections: Description Spatial Attributes Each section organizes the information concerning your dataset. 4

5 Metadata For example, if we select the Spatial tab, we see that the projection information is displayed. In the case of this dataset, the projection is UTM (Universal Transverse Mercator) Zone 12, using the North American Datum of 1983 and a spheroid of GRS80. Planer distance (display units) are meters. Metadata Metadata Quick Review: Metadata is critical to understanding important points concerning your datasets. Includes information about HOW your data was created, WHY your data created, WHEN your data was created, the SPATIAL reference your data has, WHO to contact with question, WHAT each attribute means. If creating new datasets you should generate your own Metadata (this can be done using ArcCatalog). Metadata should be maintained. 5

6 Going from this A map projection is any of many methods used in cartography (mapmaking) to represent the two-dimensional curved surface of the earth or other body on a plane. to this Geographic Coordinate System (GCS) The Geographic Coordinate System is the absence of any projected coordinate system it is not a projection! The GCS uses a three-dimensional spherical surface to define locations on Earth Earth as a Spheroid Earth is not a perfect sphere, so a spheroid provides a more accurate mathematical model of its shape Accuracy of the spheroid can be increased with more accurate measures of the axes 6

7 Earth as a Geoid A geoid is a model describing Earth s variations from the spheroid. This model is also used to further refine the accuracy of the spheroid models by introducing the datum The Datum Because of variations between actual topography and models of Earth s surface, there is a need for a more complex, more localized adjustment of the models the datum. As a spheroid approximates Earth s shape, the datum defines the position of the spheroid relative to Earth s center. The Datum A datum provides a frame of reference for measuring locations on the surface of the earth. It defines the origin and orientation of latitude and longitude lines. (Understanding Map, ESRI, 2000) Any given datum is only valid for the localized area (or region) for which it was designed. 7

8 Datum Examples Two most commonly used in the United States: North American Datum of 1927 (NAD27) Based on the spheroid Clarke 1866, uses Meades Ranch in Kansas as its origin North American Datum of 1983 (NAD83) Based on the spheroid GRS80, uses Earth s center of mass as its origin A worldwide datum, used by the GPS: World Geodetic System of 1984 (WGS84) Similar to NAD83, but optimized for global accuracy Quick Review Geographic Coordinate System (GCS) is an angular locational reference system on a sphere (i.e. latitude and longitude), Spheroid is a mathematical model of the shape of Earth Datum is a localized point of origin, defining the position of the spheroid in relation to Earth s center All three of these terms are extremely important to remember as we discuss map projections. Map A projection is a method for making a three-dimensional globe into a usable flat map 8

9 Map A visualization of a map projection There are many different projection algorithms, but almost all projections are based on one of these three basic types: Cylindrical Conical Planar (azimuthal) Map - Cylindrical 9

10 Map - Conical Map - Planar The Bad News: All Are Distorted 10

11 To some extent, all projections suffer some data loss in: Conformality (angular measure) Distance Direction Shape Scale Area The Good News: The Distortions Are Predictable It s possible to design different projections that preserve one or more of the elements, depending on need. Here are a few examples: True Direction Mercator, Stereographic, Gnomonic Conformal Lambert Conformal Conic, Polar Stereographic, UTM Equal Area Albers Equal Area Conic, Mollweide, Sinusoidal Equidistant Azimuthal Equidistant, Plate-Carrée, Simple Conic Map Coordinate Grids Once we project the spheroid onto a two-dimensional plane, we can use a cartesian coordinate system to describe locations (x,y) The coordinate grid has the advantage of consistent lengths, angles, and areas across the two dimensions, allowing for simpler measurements, e.g. Euclidian distance and analytical geometry en.wikipedia.org 11

12 Map Tangency are most accurate at the point or line of tangency (i.e. where the shape touches the globe) Universal Transverse Mercator (UTM) The UTM Projection was designed to take advantage of the line of tangency and minimize the effects of distortion, and is widely used for large scale mapping (e.g. USGS 7.5 Topos) Universal Transverse Mercator (UTM) 12

13 UTM Zones Each Zone is a long, narrow strip 6º wide It's divided by a central meridian and the Equator The limited scope of the zone helps to maintain a high level of accuracy UTM Coordinates Units=meters X and Y are called Easting and Northing UTM coordinates cannot be negative: Easting is measured from the zone s central meridian which is designated as 500,000 meters (false Easting) Northing is measured from the Equator in the Northern hemisphere and the South Pole in the Southern hemisphere UTM Coordinates 13

14 UTM Limitations While excellent for large-scale mapping within the zones, UTM is cumbersome when the area to be mapped straddles two or more zones. Since all projections and coordinate systems have their limitations, and since they are all different, it s important to know your data. Quality printed maps will indicate the datum, projection and coordinate system in the legend. Likewise, quality GIS data should include metadata. An example of the importance of knowing your projection 14

15 Riparian Monitoring Legend LCT Condition good Willow Creek Reservoir med fair/poor BLM Monitoring Locations variable Pastures non LCT An example of the importance of knowing your datum C.McGinty, E.Sant Another example of the importance of knowing your datum Quick Review: A map projection us the method used to represent the two-dimensional curved surface of the earth as a flat map. One should know the data that is being projected so the proper projection may be used. If improper projections are used, GIS, as a rule, will be useless. are one of the MOST critical aspects of geospatial data and one should ensure proper usage of the correct system. Failure to do so will result in a failure of the analysis. 15

16 Scale Measuring Distance Why does 1 mile = 5,280 feet? Well, a long, long time ago Roman: mille passum English: 8 furlongs In England, the mile was generally used for measuring the distance from one town to another Modified from McGinty & Baker, 2005 Distance Slightly Saner? The meter is perhaps of slightly saner origin One ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth) The meter is also the length a beam of light travels in a vacuum in 1/299,792,458 of a second. Modified from McGinty & Baker,

17 The Fundamental Problem Because the world is so complex, we need models to represent it. Since we have units for measuring distance, but we can t go out and measure 3,027 miles with a yardstick, we use representations. Maps are created at a representative size. Modified from McGinty & Baker, 2005 What this means Measuring distance is somewhat arbitrary. We can measure how far away (or near) things are to one another. What about when we want to measure the distance from SLC to Christchurch, NZ? Remember the Fundamental Problem Modified from McGinty & Baker, 2005 Map Size/ Scale At what size do we make our representative maps? This is the question of scale 17

18 Fractals The concept of FRACTALS was initially introduced when British map makers tried to measure the coastline of Britain. Why? Fractals Fractals contain large degrees of self similarity. Essentially many smaller copies of a fractal object are buried within itself.* The Problem as it relates to GIS: The more you zoom-in on a fractal the more detail you see. Identifies the need for acceptable scale. * Fractals GIS Example: Total Length of the Hyrum Reservoir shoreline: At 1:100,000 scale (we will learn more about scales soon) the total shore length is 5,867 meters. 18

19 Fractals Hyrum Res. shoreline at 1:63,360: 6373 meters Fractals Hyrum Res. shoreline at 1:24,000: 7335 meters Fractals Hyrum Res. shoreline at 1:12,000: 7900 meters As SCALE changes our shoreline length has continually increased. What is the true length of Hyrum Reservoir shoreline? So, why do we care about fractals? 19

20 What rule of measure are we going to use? How will it effect our spatial measurements? How will we measure if we know everything has an infinite length? It depends on our needs.. Map Scale Maps are reductions of reality. Scale is the ratio or relationship between a distance or area on a map and the corresponding distance or area on the ground (ESRI Press, 2001). The ratio of distance on the map to the same distance as it appears on the earth (DeMers, 2003). 20

21 Map Scale Representations We commonly see three types of scale represented on maps: Graphic (or bar) scale Verbal scale 1cm =1 km Representative Fraction 1:24,000 Graphical Scale Skull Valley Fire History True measures of ground distance appear on the map. Legend Number of Burns or greater Roads Highway Secondary Pasture Boundaries Miles Graphical Scale (cont.) Advantages: Graphical scales (scale bars) can be enlarged and reduced and still retain meaning. Assuming map is enlarged or reduced proportionately. Rapid assessment of distances without difficult conversions. Disadvantages: For large distances accuracy should only be trusted at center of map (although this is true for any map). Scale may be culture bound, meaning only miles are shown, only kilometers are shown, etc. 21

22 Verbal Scale Scale that is verbally expressed from one user to another: The scale is one inch equals 63,360 inches Meaning, one inch on the map is equal to 63,360 inches in the real world (on the ground). Verbal Scale (cont.) Advantage: Easy for people within one group (i.e. metric) to understand. Quick Disadvantages: May be difficult to convert cm = 2.3 kilometers (difficult to understand) Have to have ruler (or something) in hand to use. Representative Fraction (RF) Both map distance and ground distance are given in the same units. 1:24,000 Translates to 1 unit (on the map) equals 24,000 units (on the earth) 22

23 1:24,000 Representative Fraction (cont.) Representative Fraction (cont.) Advantages: Any user can utilize the map. Units are not a constraint. Quick, easy to describe. Understood worldwide. Disadvantages: Must be recalculated when map is resized. (However, this is automatic in ArcGIS) Small Scale, Large Scale? Often one of the most confused topics in map use: A small scale map would indicate that: Less detail is available on the map. A large scale map would indicate that: More detail is available on the map. 23

24 Small Scale, Large Scale? Think of it as the ratio: 1:100,000 = 1/100,000 = vs 1:24,000 = 1/24,000 = Coarse and Fine Scale Intuitive Coarse = Small scale = Large area, little detail Fine = Large scale= Small area, lots of detail Common Scales What Scale to Use? How do we know what scale to use? We (as users or creators of cartographic information) must decide what types of data we are trying to discern or relay. What is your project/ research? How large an area are you looking at? How much data are you collecting? 24

25 What Scale to Use? Examples: Mapping wood louse populations up Dry Canyon (small area, lots of individuals) Vs. Mapping moose habitat in Utah (larger area, fewer individuals) Vs. Mapping malaria outbreaks south of the Sahara (Largest area, many data points) 25