Lab 6

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1. What is the difference between selection by attributes and selection by location?
       Selection by attributes uses features to choose what to highlight, such as if a house has a pool, if the house costs a certain amount, or a river that has contaminants near it. Selecting by location lets you specify the location of one feature within a certain distance to another and then highlights everything that falls within that category.
2. What is the difference between an attribute query and a definition query?
       They are similar because for both you write an expression to find features, but features satisfying an attribute query are selected where features satisfying a definition query are displayed and the rest are hidden.
3. What steps would you use to begin a spatial join (as opposed to a join based on attributes)?
       In the table of contents, right click the layer you want to join, scroll to Joins and Relates, and click Join. In the Join Data dialog, choose "Join data from another layer based on spatial location," then select the layer to be joined.
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?
       First you have to choose select by location, then you select the features you want to use in the new layer. Afterwards, your right click the layer you are using to make the new layer and scroll to Data, then choose Export Data. Then you save it as a new shapefile and click yes if you want to add it to the current map selection or note where you saved it to use for future projects.
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?
       You would perform the steps to clip: first show the ArcToolbox Window, click the + next to Analysis Tools and then the + next to Extract. Then double click Clip. In the Input Features you'll select the layer with the features to be clipped, the features to be clipped and then the Output Feature Class. Then you'll save the new name and once it is complete, you turn off the layer clipped from which will leave you with just the selection and its clipped features, here in exercise 11 Lease F with the streams within it in tact, but nothing else around it.
6. What is the difference between a union and an intersect operation done on two polygon layers?
       Union polygons include the data in the first input, the second input, AND they're overlapping area which all take on the shape of 3 different polygons represent the different overlapping data. Intersect polygons preserve ONLY the data that is overlapped between the values in two attributes.
7. Which operation, union or intersect, can be done with a line layer and a polygon layer?
       Intersect
8. What is the difference between a geographic coordinate system (GCS) and a projected coordinate systerm (PCS)?
       GCS is a system that defines locations on the curved surface of the earth whereas PCS defines locations on a flat map using x,y coordinates.
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?
       ArcToolbox
10. Where do you find out what projection the data is in? (Hint: This is "data about data.")
       You can find it in ArcToolbox under Data Management Tools, Projections and Transformation, Define Projection. If it is unknown then you have to choose. Also, it can be found in the Metadata in ArcCatalog.
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?
       Lambert Azimuthal Equal Area