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.