Lab 6 Exercises

1. What is the difference between selection by attributes and selection by location? 

2. What is the difference between an attribute query and a definition query? 
   
    "A definiton query resembles an attribute query is  that you write an expression to find features with particular attributes.  The difference is that features satisfying an attribute query are selected, while features satisfying a definition query are displayed and the rest are hidden" (Ormsby 267).
3. What steps would you use to begin a spatial join (as opposed to a join based on attributes)?

4. If you want to select part of an existing layer (or shapefile or geodatabase) and create a new shapefile or geodatabase out of it that actually exists as a separate data file that you could put into another map document file, what two functions do you have to choose from? 

5. If you just want to take selected features from an existing layer and display them as a separate layer within the current map document file without creating a new data set, what steps would you perform? 
6. What is the difference between a union and an intersect operation done on two polygon layers? 

7. Which operation, union or intersect, can be done with a line layer and a polygon layer? 
8. What is the difference between a geographic coordinate system (GCS) and a projected coordinate system (PCS)? 

9. Let’s say you obtain a spatial dataset off the web and add it to an ArcMap file you are working on, but in the process you get the error message shown on p. 348 stating “One or more layers is missing spatial reference information.  Data from those layers cannot be projected.”  What application or program do you use to tell ArcGIS what projection the data is in? 

10. Where do you find out what projection the data is in?  (Hint: This is “data about data.”) 

11. For practice with this, go to the National Atlas Map Layers Warehouse (http://www.nationalatlas.gov/atlasftp.html).  What map projection is used for the “Land Cover Characteristics” GeoTIFF file?