The next set of labs for people on the urban and regional planning  track will all use the same data set. The data exists as a set of Arcinfo coverages at this location:

N:\LABS378\fitchb

All this data is in Arcinfo export format so you will have to copy it over to your workspace and import it using Import 7.1 (from the ESRI program group)

The instructions for these labs are much less detailed than the first set of labs because you should not have to be "walked through" the commands, menus and buttons to do the tasks. To help you out a little I have included in brackets the previous labs where you did work like this so you could go back to the lab and figure it out. But what I really want you to do is to become a little more adventurous with the software and seek out what is behind the buttons and menus.

These labs are not designed as units. As soon as you have completed the tasks e-mail me your reponse. This may be the location of a project file for Arcview, a table you created, etc. During lab time I will be around to trouble shoot and help you find things but if you ask for help, my first question will be "Show me what you have tried already." In other words, I want you to fumble around the data and software for a while before you call me over and be able to explain what you have done so far. Remember - you cannot hurt the data or the software. The worst it will do to you is tell you it can't execute the command you want it to. So… have fun!

Files needed: You will need the Zoning.e00 and Ward.e00 files for this task. You will find them in N:\labs378\fitchb.  Create a workspace for yourself, copy the export files in and import them to make them coverages.

The planning executive director is having a set of neighborhood meetings by ward around the town. Everybody likes to have data customized for their area and GIS is an excellent tool to do this. You have been asked to prepare some tables showing how much of each ward is covered by each zoning category. You will have to create a new field acres and calculate that field based on zoning (there are 43560 feet in an acre).  As in Core Lab 2 you will use the Field/Summarize option to add up the square footage of each zoning category, convert them to acres, use Field/Statistics to find the total number of acres and then calculate the percentage.

A. ENTIRE CITY

B. Acres of Zoning  By Ward

Because some of the zoning polygons are very large they interesect many different wards so just selecting a ward and doing Theme/Select by theme and then summarizing the acreages is going to give you some weird results.  If one corner of a large zoning polygon intersects a particular ward, the entire zoning polygon is selected and that is not what we want.

As with many problems, there are multiple ways to solve this.  Choose the one from the list below that you want to work on.

1. Using Spatial Analyst - create grids of zoning and wards.  You will have to turn them into shapefiles first (under the Theme menu) and then load spatial analyst.  Grid them as 50x50 ft grid cells and make sure you cover the entire city and use the same theme as the spatial extent for both grids.  The process you will have to use will create a lot of grids so make sure you keep track of them and give them informative names; it is very easy to fall into the trap of using default names and the not knowing what is what.  You will need to assign a number to each zoning category and to each ward because when you use the map calculator to multiply them together (as you did in Core Lab 2) you need numbers since the multiplication of 1A * CBD is not a defined multiplication.

Make a separate grid for each ward using a 1 for a cell if it is in the ward and No data if it is not,  and multiply that times the zoning grid (using a number for each different zoning category).  So if RA1 is the 10th different zoning category in the grid of zoning, each cell in that zoning area has a value of 10.  And if you are working with ward 1A, all grid cells in that layer that are in ward 1A have a value of 1 and those that are not have a value of no data.  The resulting map calculation of zoning times ward 1A will give a grid with counts for each zoning category.  Then you will calculate square footage and acreage as above.

2. Using the Geoprocessing Wizard in Arcview

Arcview has some limited overlay functions housed in the Geoprocessing extension which you load like any other extension.  The only difference in the interface is in the View menu where "Geoprocessing Wizard" becomes an option.  You would bring in the zoning and ward themes and choose to Union them.  The process is simple but interpreting the output is not.  Two problems are created:

A. Sliver polygons - after you do the union operation, build a query and search for the polygons in the union coverage that do not have a ward number, i.e. ([ward] = "").  Depending on the order in which you did there may be a different number but I got eleven.  If you select one of them and try to find it you will discover they are extremely small - less than .01 feet across in some cases - polygons around the edge of the theme.  Solving the problem - you could turn editing on, select those by a query and delete them from the theme.  This removes them from the table as well so that every polygon has a ward value and a zoning value.

B. Calculation of Area - since the union function attaches the attributes of both tables to the unioned table there will be two area and perimeter fields - one from zoning and one from wards.  But the information in them are the areas and perimeters from polygons in those two tables, NOT the areas and perimeters from the newly created polygons produced by unioning. Solving this problem requires running a script that is hiding in the help function. From the help function, look fo View.CalculateAcreage(Sample Script).  Cut and paste this script into a script window, compile it and run it on the union theme.   It will calculate the acreage BUT.... this is a complex process so make an appointment with Dr. Harmon if you want to do this.  There is also an error in the script in converting from square feet to acres that needs to be fixed.  But... it works.  After getting the script compiled and run to calculate the areas of the polygons created by unioning the zoning and ward themes you will need to build a query for each ward and use the Field/Summarize function on the zoning categories.  You will want to summarize Acres by sum.

3. Using Arcinfo

If you have access to Arcinfo it is the easiest way to do this.  The UNION command is found in the ArcToolbox Analysis set of tools.  Specify one of the coverages as the input coverage and the other as the union coverage.  This will create the union of these two coverages (the area covered by both coverages) with the attribute information of both attached. The area for the union polygons (all the 218 unique Ward/Zone combinations) will be correct. Using Union from the Arcview geoprocessing wizard, you will get the areas from the parent polygons in the two layers, Wards and Zoning but not the area of the new polygons.

To get a feel for the sliver problem, select by attribute all those polygons in the union coverage that have an area  less than 100 ft. and zoom in on a few in the map window.  You will see several odd-lookig polygons.  If you had used Spatial Analyst and 

To calculate the areas of zoning categories for each ward you will first need to calculate the acreage for each polygon in the union coverage. [Turn editing on, add a field called acreage - number, 8 columns wide, 3 values to the right of the decimal point. Use the Field/Calculate menu item to calculate Acreage = Area / 43560].  Then you select the wards, one at a time [Use the query builder], highlight the zoning category field.  Use the Field/Summarize option with Field: Acreage, Summarize by: Sum.  Add this to the table (make sure the table will be saved in your lab workspace) and click OK.  This will complete one row of the table.Do this for each ward to complete the table.

                         Acreage Table to be completed.

Turn in...

1. The location of your project. Make sure all objects such as views, tables, etc. have real names and not view1, etc.

2. A printout in Excel or just on paper of the three tables. If you have created a spreadsheet, e-mail that to me as well.