Lab 6

February 16, 2004


Chapter 10 Questions:
(A) What is the difference between selection by attributes and selection by location?  
       Selecttion by attributes is finding feature of similiarities among attributes. In selection by location, it is a spatial relationship to other features
(B) What is the difference between an attribute query and a definition query?  
       An attribute query looks for features and this is where the dialog box and the typing in the equation occurs. In a definition query, it can be used for outside                 sources and this is where just the equation appears.
(C) What steps would you use to begin a spatial join (as opposed to a join based on attributes)?  
       First right click on the target layer-join or relate tab-then click the join button. Select the desired feature and click join.



Chapter 11 Questions:
(D) If you want to select part of an existing layer and create a new layer out of it that actually exists as a separate data file that you could put in another map document file, what two functions do you have to choose from? 
       Two option, a personal geodatabase or a shapefile
(E) If you just want to take part of an existing layer and display it as a separate layer within the current map document file, what steps would you perform? 
       Use the geoprocession wizard then select the options or the desired features to create the new layer and click finish.


Chapter 12 Questions:
(F) What is the difference between a union and an intersect operation done on two polygon layers? 
       A union is non-overlapping areas that are included in the new data set. An intersect is only the coincident geometery that is perserved.
(G) Which operation, union or intersect, can be done with a line layer and a polygon layer?
       An intersect

Chapter 13 Questions:
 (H) What is the difference between a geographic coordinate system (GCS) and a projected coordinate system (PCS)? 
       The GCS only uses latitude and longitude as its features for mathmatical calculations. The PCS uses mathmatical transformation of data for its math calculations.
(I) 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. 340.  What application or program do you use to tell ArcGIS what projection the data is in? 
       I would use the Definition Projection Wizard that is located within ArcToolbox.
(J) Where do you find out what projection the data is in?  (What is “data about data” called?) 
       It is located in the metadata.
(K) 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? 
   The Lambert Azimuthal Equal Area projection.   Natioal Atlas Website