Our local data sets are large files and can take more time to display than you care to wait. You can create separate subsets of a data set and save  it to your own folder, so that you not only save time but have copies of your own to modify and use.

There are two methods you can use. One is to select a portion of an existing shape file and export that to a new shape file. The other is to clip an existing shape file by using another polygon shape file (like using a cookie cutter) to create a new shape file.  If you use the selection method, you will come out with entire features, e.g., entire parcels, or entire road segments, so some of these may extend beyond the area you want. If you use the clip method, all features are clipped at the border of the cookie cutter. This has the advantage of not including anything outside your area of interest but the disadvantage of chopping some features up which perhaps should not be chopped (e.g., parcels).

To create smaller subset data set of larger data set using the selection method:
In the selection method, you first select features from a larger data set, then export those selected features to a data file.

• In ArcMap, add all the data sets for which you want to create subsets

• Check to make sure that all these data sets are selectable by choosing Selection-Set Selectable Layers. Checkmark all the datasets for which you want subsets. Press Close.

• Find the Tools toolbar - depending on how the last session ended, this may be in different places on the screen. If it is not visible, choose View-Toolbars-Tools
  
  

• Press the Select Features icon ()  

• The easiest method for selecting is simply making a box to mark the project area (click and hold the mouse key in the upper left corner of the area, drag down to the lower right corner and release, just like making a zoom-in box). Alternatively, you can point and click at a feature. To add more features to the selection, press the Shift key and point to another feature. To delete a feature from a selected set, you can press the Shift key and click on that feature. Basically, keeping the Shift key pressed allows you to add or delete features to a selected set. There are a number of ways to select features in a map -  to find out more, in ArcMap, choose Help-ArcGIS Desktop Help, click on the Contents tab, and go to ArcMap-Querying Maps, and look at the different entries about selecting.

• Once you have the features selected that you want in the new subset data file, you can start the exporting process. You must export data for each data layer. To do this, right-click the data layer containing selected features and choose Data-Export

• For Export, make sure that Selected Features is the specified option.

• Specify how you want a coordinate system defined for this new data file (probably same as the source-original data).

• Navigate to your personal project folder and give this data set a new name (e.g., parks_clip)
  
  
  This will create a new shape file with only the selected features.
  

• Repeat this process for every data layer for which you want a smaller subset.

• When finished, make sure that all your new data sets are working and viewable in ArcMap.

• Quit ArcMap
• You can delete the original large datasets you no longer need by going into ArcCatalog, highlighting theses datasets and pressing the delete key on the keyboard. Don't try this with the data layers still up in ArcMap. In general, ArcCatalog is the best place to delete, move, or copy data sets rather than Windows Explorer or File Manager. Some GIS data sets (like ArcInfo coverages) have more than one file and folder. Using ArcCatalog to manage files keeps these files intact.

To create smaller subset data set of large data set using the clip method:
Note: the following instructions do not work in ArcGIS 9, our current lab software version. There is a clip tool in the ArcGIS 9 Toolbox under Analysis Tools - Extract - Clip. See the directions for using it. You will still need a "clipper" file as described below.

To use the clip method, you will need to have a polygon shape file which will act as the "clipper" (the cookie cutter) in addition to the "clippee" shape files. This could be an existing file like watersheds - in that case, select the watershed which will be your boundary area, and then perform the clip as outlined below. If you don't already have a shape file to use as the "clipper", you need to create one. It needs to be a polygon layer (e.g., a simple square covering the area you want to clip, but it could also be an irregular feature) - see Creating a new boundary feature below.

Instructions for ArGIS 8 (not 9):

Once you have a boundary file to use as the "clipper" file, load either the Geoprocessing extension Then you can use the Clip function of either extension - just follow the prompts carefully to select the "clippee" and the "clipper" shape files. Also be careful where you are putting the newly made files - by default they will be called something like "clip1.shp" and be placed in the C:\temp\ drive. Give them a better name and put them in your own folder. You will have to go through the clipping process one time for each shape file you want to clip.

Note: New geographic files must be created in ArcCatalog - for clipping to work correctly, both the file to be clipped and the "clipper" file need to have their map projection/coordinate system defined. Be sure you have done this (see Defining a Projection in ArcToolbox for instructions).

Creating a new shape file in ArcCatalog:

• Start ArcCatalog (Start-Programs-ArcGIS-ArcCatalog
• In ArcCatalog, navigate to the folder in which you want to create/store your new boundary feature
• Choose File-New-Shapefile
• Give the new shape file a name (e.g., project_clip) and specify that it is a polygon feature type
• For coordinate system, choose Edit.
• In the next coordinate  system definition panel, choose Select
• Next choose the coordinate system you want to use - it should match the coordinate system of your data, or a majority of your data sets. For us this is usually either State Plane, NAD 83 (feet), Texas Central Zone or UTM, NAD83, Zone 14N.  Both of these can be found under the Projected Coordinate Systems folder. When you have highlighted the coordinate system you want, press Add
• Back in the Coordinate System definition panel, press OK
• Press OK again to finish creating the new shape file
• You now have a new shape file, but it does not yet have any geographic features in it. To create a geographic feature in this shape file, you need to go to ArcMap

Creating a new geographic feature in ArcMap:

• Open ArcMap and add the geographic data you want to clip (you must have already defined the projection for these files)
• Add the new boundary file you just created (e.g., project_clip.shp) - you are going to edit this shape file to create a new polygon in it that is your "clipper" polygon
• Bring up the Editor toolbar by choosing View-Toolbars-Editor
  
  
• Find the Editor toolbar, and choose Edit-Start Editing. The file you want to edit is your new clipper file (e.g., project_clip.shp). When asked which folder it is in, choose the folder that contains that file  and press OK (you can click through the folders if you're not sure - you will eventually see the name of the clipper file).
• Make sure that on the Editor toolbar, the Task says Create New Feature, and the Target is your "clipper" file, like this:
  
  
• Before going on to the next step, make sure you can see the entire area that will be covered by the clipper polygon, and remember that you may want your clipper polygon to include a little bit outside the area for context (e.g., if your area is bounded by four streets, it may be better to include a 100 feet or so beyond each street centerline).
• You are now ready to create the new feature. To do this, click on the Pencil icon (make sure to choose the Pencil, not the other editing tools)
  
  
• Place the cursor on the map where you want to begin your new polygon feature - you should see a circle with a cross-hair in it, and click once. Then go to the next point that defines your polgyon and click again. Continue doing this until you are almost back to the last point. To close the polygon, double-click on the next-to-last point, or press F2 after the next-to-last point.  If you get messed up, you can either double-click to finish, and then press the Delete key on the keyboard, or you can right-click and choose Delete Sketch. It may take a few attempts to get it right.
  

  Adding vertices to a polygon in an edit sketch - add as few points as you need to define the polygon (e.g., a box would need only four points on each corner	A completed polygon in an edit sketch - the blue outline indicates that it is selected, so if you don't like it, you can press the delete key on the keyaboard

• When you have a boundary polygon complete for your area, choose Edit - Save Edits.
• Get out of editing mode by choosing Edit-Stop Editing - you now have a "clipper" shape file ready to clip your other data sets

Clipping project data sets (note the procedure below does not apply to ArcGIS 9.x which does not have the geoprocessing wizard):
Note: You will have to go through the clipping process for each shape file you want to clip. You cannot clip multiple files at once.

The clipping process is done using ArcGIS Geoprocessing Tools.

• In ArcMap, choose Tools - Geoprocessing Wizard
• Select the Clip One Layer Based on Another option. Read More about Clip before you proceed.
• When you are ready to proceed, choose Next, and follow the prompts carefully to select the "clippee" and the "clipper" shape files (see figure below). Also be careful where you are putting the newly made files - by default they will be called something like "clip_output.shp". Give them a better name and put them in your personal project folder.
  
  
• Continue this process for each GIS data set you want to clip.
• When finished, make sure that all your newly clipped data sets are working and viewable in ArcMap.
• Quit ArcMap
• You can delete the original large datasets you no longer need by going into ArcCatalog, highlighting theses datasets and pressing the delete key on the keyboard. Don't try this with the data layers still up in ArcMap. In general, ArcCatalog is the best place to delete, move, or copy data sets rather than Windows Explorer or File Manager. Some GIS data sets (like ArcInfo coverages) have more than one file and folder. Using ArcCatalog to manage files keeps these files intact.