GEOG 206: Intro to GIS

Fall 2010

1. What are some advantages and disadvantages of using digital spatial data?

Advantages:

·         Distributed at low or no cost.

·         Easiest and quickest to access.

·         Direct digital collection eliminates data transfer to viewable physical media such as maps or written lists.

Disadvantages:

·         Free data you get from sources (e.g. ESRI) is free but not up to date.

·         To use current data you often have to pay companies.

·         Free of charge data is often in large pixels. This means the resolution is not the greatest.

2. What are the most important questions you must ask before using already-developed spatial data?

ü  What was the purpose or intent for collecting such data?

ü  Who collected the data? (IS it a reliable source?)

ü  What do you want to use this data for?

ü  What type of data are you trying to find? (E.g. what’s the purpose of the study? Are we studying vegetation, population, topographic information?

ü  Do we want to use national or Global Digital Data?

3. How do DOQs differ from regular photographs?

·         DOQ’s are scanned photographic images that have been corrected for distortion do to camera tilt, terrain displacement and other factors (geometrically corrected images). They are also registered to an earth coordinate system. This means that they combine the scanned image with ground coordinate information to remove positional errors. IT also removes geometric distortion due to camera tilt, camera systematic errors and terrain displacement.

4. Choose three existing data sets and describe who produces them, what the source materials are and what they contain.

v  National Wetland Inventory (NWI).

Produced by: US Fish and Wildlife Service.

Source materials: field visitation and interpretation of aerial photographs, spring photographs at a range of scales and types are used. This system uses minimum mapping unit (MMU) which is the target size of the smallest feature captured.

Contain: It contains information on wetland types. They are categorized as lacustrine (lake), palustrine (pond) or rivenine. Then a subsystem specifies further attributes.

v  Digital Floodplain Data.

Produced by: The federal Emergency Management Agency (FEMA) develops and disseminates floodplain maps. This digital floodplain maps are produced by cooperating technical partners (CTP) to define regions within a 100-year floodplain.

Source materials: GIS, the use of LiDAR, datum conversions and the analysis and 

mapping of specific landforms.

Contain: maps that show regions that are most susceptible to flooding. It shows flooding hazard  

areas.

v  Tiger Census Data.

Produced by: Census Bureau.

Source material: Tiger/line is organized in 17 different record types. It reports the location and attribute information about a census feature. GIS is software that is commonly used by the census. They convert TIGER/Line and related Census files to data layers in specific GIS formats.

Contains: These files contain attributes for lines and area features which include county boundaries, school district, City Township, parks, infrastructure and many other information for city management and federal government activities.

5. What is the difference between DEMs and NEDs?

DEMs:

ü  Produced using photogrammetric techniques.

ü  Ground and aerial surveys are the primary source of original elevation measurements. (this method is slow and can only provide a spare network of points.)

ü  Small areas are seen in very high resolution.

NEDs:

ü  Newest technology to create elevation maps.

ü  Also known as LiDAR is based on a downward pointing laser placed on an aircraft. ( Often used when presided elevation measurements are required

ü  NED is an improvement over previous sources because it is a high resolution, flawless data source.

ü  Such flawless data avoids problems with gaps or discontinuity.

  

Step through the following instructions and answer any associated questions.

1. Launch ArcCatalog and navigate to the T drive. Copy the following GIS data down to your Lab5 folder on the C drive (or U, Z, I, etc.).

a. USGS 1:24,000 Topographic Quads: T:\\gis_data\usgs\quad_grids\topoq24.shp

b. LA County Landuse: T:\\gis_data\miscellaneous\socal_landuse_2000\Los_Angeleslu_2k\lacounty_lu01.shp

2. Go to my folder for Geog206 on the Y drive and copy the Lab5Data.mdb geodatabase down to your Lab5 folder. Explore the geodatabase.

a.       What are the names of the feature datasets in the geodatabase?

ü  Base-map

ü  Hydrology

b.      What are the names of the feature classes in the hydrology dataset?

ü  NHD Flowline

ü  NHDPoint

ü  NHDWaterbody

ü  Watershed

c.       For each one of the feature classes you just listed, describe whether it is a polygon, line or point layer.

ü  NHD Flowline – line               

ü  NHDPoint-point          

ü  NHDWaterbody- polygon       

ü  Watershed- polygon

3. Using ArcCatalog, answer the following questions.

a.       Is topoq24.shp a raster or vector layer?  

b.      What is the GIS data format of topoq24.shp?

ü  Shapefile

c.       Is there metadata associated with topoq24.shp?

ü  yes

d.      What is the GIS data format of the NHDFlowline layer?

ü  Geodatabase

e.       Is there metadata associated with NHDFlowline?

ü  yes

f.       What are 3 keywords used to describe the NHDFlowline layer?

ü  Hydrography, stream/river, lake/pond.

g.       Who created the NHDFlowline layer?

ü  US Geological survey in cooperation with US Environmental Protection Agency, USDA Forest Service and other federal, state and local partners.  

4. Export the NHDFlowline feature class to a shapefile format, name it NHDFlowline.shp and place in the Lab_5 folder on your C-drive.

a.       Is there still metadata associated with the layer?

ü  yes

5. Open ArcMap and load the following layers. topoq24.shp, CountyBoundaries, Highways and lacounty_lu01.shp. Save the ArcMap document in your Lab5 folder and name it Lab5.mxd.

6. In the next step, you will use the topo layer to figure out which DOQQ to download from the CASIL website so that you can view the CSUN campus.

a. In ArcMap, open the attribute table for topoq24.shp.

b. In the USGS_QD_ID field, find the value that corresponds to the Canoga Park QUAD_NAME. What is it? __34118-B5______________

c. Click on the following link:

http://archive.casil.ucdavis.edu/casil/remote_sensing/doq/doqq/

d. Use the first 5 digits of the USGS_QD_ID value to figure out which folder to go into.

e. Once in the folder, you want to download the canoga_park_ne DOQQ.

Note: You can sort the quad names by clicking on the Description field.

Note 2: For each DOQQ you download, you will need the .tif, .tfw AND .tif.xml files.

f. To download: Right-click on each file separately and choose Save Target As. Make sure you save to the Lab5 folder on your C-drive.

7. Load the DOQQ tiff into your Lab5 ArcMap document. Is the DOQQ black and white or CIR (color infrared)?

ü  Black and White

8. Use the DOQQ and Highways layer to find the CSUN campus. Zoom to that location. Capture a screenshot (Alt+PrintScreen) and paste into a Word document with your other answers for this assignment.

9. Save your Lab5.mxd document and close ArcMap.

10. In ArcCatalog, navigate to your Lab5 folder. Capture a screenshot (Alt+PrintScreen) of the expanded folder/file structure and paste into a Word document.

11. In ArcCatalog, navigate to the Lab5 folder and rename lacounty_lu01.shp to La_Landuse.shp. Note: You will not be able to do this if ArcMap is still open.

12. Open the Lab5.mxd document again.

a.       What happened to the lacounty_lu01.shp layer?  

ü  The Layer is grayed out.

       b. Fix the problem by redirecting the layer to the new data source name.

PROJECTING THE GLOBE

 

Coordinate Systems & Projections

1. What is an ellipsoid? How does an ellipsoid differ from a sphere?

A.      An ellipsoid is a sphere slightly flattened at the poles.

B.      A sphere in geometry is “The set of all points in three-dimensional space lying the same distance (the radius) from a given point (the centre), or the result of rotating a circle about one of its diameters. Now an ellipsoid is sometimes referred to as a special class of spheroid known as “oblate” spheroid. You can refer to an ellipsoid as a type of sphere.

Definition of a sphere taken from <http://www.answers.com/topic/sphere>

2. What is the imaginary network of intersecting latitude and longitude lines on the earth's surface called? 

•  The lines of constant longitude are called meridians and the lines of constant latitudes are called parallels.

3. How does the magnetic north differ from the geographic North Pole? 

•  The Magnetic north is the location towards which a compass points. The geographic North Pole is the northern pole of the Earth’s axis of rotation. For map projections and coordinate systems the geographic North Pole is the one used.

4. Why are datums important? Briefly describe how datums are developed.

·         A Datum is a reference surface. They are important because along with astronomical measurements that have been done on the earth’s surface, datums are used to specify the coordinate location of points on the surface of the earth.

·         Datums consist of two major components which are:  a specified ellipsoid from the particular area being studied and a set of points and lines that have been surveyed thoroughly with specific coordinate locations specifying horizontal positions or vertical positions on the surface of the Earth

5. What is a map projection?

• Map Projection is a systematic rendering of locations from the curved earth surface onto a flat map surface.

6. What is a developable surface?

• A developable surface is a geometric shape onto which the earth’s surface locations are projected.  Cylinder, cones and planes are the most common developable surfaces. The orientation of developable surfaces can change among projections and vice versa. Most common map projections on GIS are based on developable surfaces.

7. Which lines on the graticule run north-south, converge at the poles, and mark angular distance east and west of the prime meridian?

ü  Lines of longitude

b. The major axes

c. Parallels

d. Lines of Latitude

8. Which of the following ellipsoids is now regarded as the best model of the earth for the region of North America?

a. Clarke 1866

b. International 1924

ü  c. GRS80

d. Bessel 1841

9. Which well known coordinate system would be appropriate to use for developing and analyzing spatial data when mapping counties or larger areas? Why?

·         The State Plane Coordinate System based on two types of map projection which are Mercator and Lambert.

§  It is appropriate to use these two types of systems because distortion typically increases over large distances. This system provides a common coordinate reference for horizontal coordinates over county to multi county areas while limiting error to specified maximum values. Projection distortions are very low.

10. What is a great circle distance?

• The great circle distance is a distance measured on the ellipsoid and in a plane through the earth’s center. This planar surface intersects the two points on the earth’s surface and splits the spheroid into two halves. The formula is use to find the distance distortion caused by a projection between two points. Such calculations are approximate because we base the assumption of a spherical rather than ellipsoidal earth.  Pg96   

                 The Importance of Map Projections

Map projections are ways of transferring information from a 3 dimensional sphere to a 2 dimensional plane. This becomes important to anyone working with GIS or any other geographic system because we cannot perfectly represent a three dimensional object in two dimensions. In other words we use it to represent the earth on a flat surface.  As mention earlier, since the world is a type of spheroid when you project it on a map it will undoubtedly create some type of distortion.  When we choose a map projection it lets us control the type of distortion for the particular area of interest.  There are four characteristics that a type of projection will distort. These are shape, area, distance and direction.  For example, the Mercator and Gall Stereographic is a conformal map projection I used to create two of my maps. This type of map projection preserves shape but distorts area. This is why on the map Alaska looks bigger than Brazil. The distance from Washington DC to Baghdad is distorted because this particular projection is not preserved in that direction. Equal area projections such as Bonne (World) and Sinusoidal, preserve area but distorts shape. The proportional sizes of Brazil and Alaska are correct yet the shapes are not. The distance from Washington DC to Baghdad is approximately 6199 miles. Out of the eight map projections I used, the ones that gave me the correct miles from Washington DC to Baghdad where the Sinusoidal, Bonne and the Equidistant Conic. This is because on such projections distortion of distance is lower near that direction. It all has to do with the way you project the globe to a flat surface. This all begins when an unrolled cone or cylinder intersects the ellipsoid (The best representation of the globe so far). At the point of intersection standard “Parallel Lines” form, and the distance is less distorted here. All of this is done through a series of mathematical calculations. On the Equidistant Cylindrical map projection if you take a look the shape of the countries they look very odd. When I measured the distance between Washington DC to Baghdad it was also distorted. The reason for this is because Baghdad is not at a close distance from Washington DC. In this type of projection near distances are preserved but far away ones are distorted.

Distortions take different forms depending on which area of the map you are looking at. There are only a few places on a map where distortion is zero and where the length, direction or shape of an area is preserved. Distortion usually increases when distance increases. There is an area on a map called the “line of true scale” and this is the area where there is no distortion happening. However, as you move away from this scale all properties start to change and begin to get distorted. Among the many map projections used out there we have two that are the most commonly used. These are the Lambert Conformal Conic (LCC) and Transverse Mercator. There are a series of mathematical measurements and implications behind every single map distortion. Yet the most important thing I take from this is that choosing the right projections is up to the particular area you select to study.  



Lab #3: Data Formats & Models

Geog 206: Intro to GIS

Fall 2010

I. Answer the following questions based on Bolstad Chapter 2 and lecture.

1.       A. What is a data model? It is defined as the objects in the spatial database plus the relationship among them. Model in this case is used to describe many things.

B.      Describe the two most commonly used data models.

·         Vector Data Models and it uses discrete elements such as point’s lines and polygons to represent the geometry of real world entities.

·         Raster Data Models and it defines the world as a regular set f cells in a grid pattern. They are spaced in an x and y direction.

2.       What is topology and why is it important?

Topology is the study of geometric properties that do not change when the forms are bent, stretched or undergo similar geometric transformations. It is important because it has great analytical capabilities. In other words they explicitly record the connection of a set of pathways and so it facilitates network analysis. Overlay operations are also improved when using topological vector models. 

3.       What type of data model would be best for representing hillside slope? Justify your answer.

Raster Data Model is the best representation of a hillside because a hillside slope is a continuous spatial feature best represented in this type of data because it simply represents the variations in a changing surface.

         4. Describe the relationship between spatial detail and cell dimension with regard to raster models.

First it important to understand that as the number of cells required to cover a given area increase dramatically as the cells dimensions get smaller. The smaller the cell the greater the spatial detail. The cell dimension affects the spatial precision of the data set and hence the accuracy. A coordinate applies to the entire area covered by the cell so the point is usually defined at the center of the cell. This means that positional accuracy could be no better than once half of the cell size.

5.       What are the four types of attribute data? Give an example of each.

§  Nominal = descriptive/categorical data

ex. Film clips, audio recording, other descriptive information.

§  Ordinal =   ranked/ordered data

ex.  Getting first, second or third place in a race.

§  Interval = ordered data, with absolute differences in magnitude and arbitrary zero

ex.  temperature

§  Ratio =ordered data, with absolute differences in magnitude and absolute zero

ex.  Weight, distance.

6. List two types of vector data file formats.

·         DXf autodesk (.dxf)

·         MIF/MID mapinfo ( .mif, .mid)

7. List two types of raster data file formats.

·         MIF/MID mapinfo ( .mif, .mid)

·         GeoTIFF, workgroup (.TIF, .TFF)

II. Answer the following questions using the data/tutorials supplied in Ormsby

Chapter 4.

8. You can do all of the following in ArcCatalog EXCEPT:

ü  Identify features

b. Copy data

c. Select features

d. View metadata

9. In the Chapter 4 exercises, does the World.mdb geodatabase contain a feature dataset?

                Yes it does.

10. What are the names of the feature classes contained in the World.mdb geodatabase?

                Cities, countries, disapp_ area, word30

11. What data format does the flight_path.lyr layer file reference?

                It has to reference to the flight_ diverge shapefile.

12. What are two ways to add data to an ArcMap document?

                A. From Arc catalog drag the data to Arcmap. Once it’s there you can look at it as a map display and Table of Contents.

                B. Click on the insert menu and click data frame. In addition you can right click a specific layer and click copy, then right click on the new data frame and click past layers.    

13. How many features (records) exist in the dissap_area feature class?

              699 feature records

14. How can you determine this using ArcCatalog?

       Go to metadata in ArcCatalog -> attribute ( click on it and it will tell you the details for the countries).

      

  

Learning The Basics of ArcGIS

1. What types of software products are included in ArcGIS and which one will we be using most in this course?

ArcGIS Desktop, Mobile GIS, Server GIS, Online GIS, ESRI Data. We will be using ArcGIS desktop the most.

2. Would it be better to perform most of your data analysis and layer symbolization in
data or layout view? Why?

It would be better to perform data analysis and layer symbolization in Data view because layout view represents an outlook of the printed page. You can add tittles, scale, bars legends and other elements. With data views you can create analyze and symbolize maps.

3. What are two ways to obtain help for ArcGIS Desktop?

You can go to the main menu and scroll down to the icon “What’s this?” or just press shift+f1 or go to support.esri.com.

4. How are attributes linked to geographic features?

 A geographic object in a layer such as a city, a country, a lake and even temperature are all called features. They are just represented in a variety of shapes and they tell you everything about a layer. However, there is much more to a feature and its shape and location. We might be curious about the country’s population, capital system of government, ext. There is a lot of information to be had in a feature. This is why GIS stores information about the features of layer in a table. It keeps record of everything in the feature of the layer. These categories are called attributes. Attributes help describe and define a feature we wish to represent in GIS.

5. What is the file extension of an ArcMap document?

The file extension is map document’ or ‘.mxd’.

6. What are two ways to zoom in/zoom out on a map?

 In the tools toolbar click on the zoom in or out tool you will be able to perform this task. The map zooms to its original extend if you click the “Full extend button” icon on the tools toolbar. Another way to zoom in and out is by clicking on the pan tool also located on the tools toolbar. The only thing you have to do is roll the mouse up or down. Another way is to just go to tools on the main menu and look for the zoom icon.

7. List three operations available in the ‘context menu’ of a layer. Hint: Right‐clicking with your mouse in the TOC should help you with this question.

Three operations available in the context menu of a layer are the layer’s property, Opening the attribute table and converting features to graphics.

8. If the check box next to a layer in the table of contents is grayed‐out, what does this mean? How would you resolve this issue?

It means that the layers visibility depends on the map’s scale. To resolve this issue you just have to zoom in and the layer will become visible.

9. What are the differences between large and small scale maps? Provide an example of each.

Large ground areas create small scale maps. For example, a map of the United States.
Small ground areas create large scale maps. For example , a map of your block.
The reason for this is because in a small area the fraction is very small.

10. Describe the differences between features and surfaces. Provide an example for each.

Features: are descriptions in this case geographical descriptions that we wish to represent in GIS. For example a city a river, a lake.

Surfaces: Is more of a continuous expanse that changes from one collection to another. For example the ocean is a geographic expanse that does not change from one location to another, unless we are talking about different water depths.

11. A GIS is a useful problem‐solving tool. You can do all of the following tasks with it, except one. Which one?

1.  Create project criteria
2. b. Query data
3. c. Display data on a report
4. d. Store project data

Using the existing ArcMap document “Ex03c.mxd”, and the knowledge and skills you have gained from the Chapter 3 exercises, answer the following questions:
12. What are the minimum and maximum elevations of the cities Earhart visited? Briefly describe how you determined these values.

The highest maximum elevation was 1045 the city of Tucson the lowest elevation out of all the cities she visited was the New Orleans, USA with a 0 elevation status. I determined this by doing a right click on the layer called “Cities Earthhart Visited” and then I opened the attribute table.

13. On the continent of Africa, what is the approximate distance (in miles) from Dakar to Assab? What are two techniques (one tool and one process) you could use to figure this out?

It is approximately 5740 miles. One way to figure the approximate distance out is by clicking on the Tools toolbar and the clicking on the measure tool then with the drop down menu we can point to distance and click kilometers, meters or in this case miles.
14. What are two possible methods you could use to figure out the names of the cities shown on the map?

Two ways this is done is by clicking in the identify tool in the tools tool bar and click the city you want to identify. It gives you all the information about the country. You can also simply click on the cities layer located in the TOC and right click. Then open the attribute table and just highlight any city you wish to know the location of.

15. Zoom to the extent of North and South America so that all the cities Earhart visited are labeled. Capture a screen shot (Alt + PrtScr) of this view and paste into your Word document (Ctrl+v). Turn in this screen shot with your answers from this sheet.