This tutorial discusses the planning and implementation of a GIS project. The particular problem to be solved is to find a suitable location for a new wastewater treatment plant.

As the city of Greenvalley grows, additional wastewater treatment is becoming necessary. A new treatment plant and recycling facility will be built.

Planning the project

Identify objectives

The location for the current plant was chosen by the city council based on general knowledge of the area and assistance from the city engineer. This approach requires a large amount of time and has little opportunity for public input. The area is now much more developed and there are many additional environmental and public health regulations that must be followed.

The approach to be used will identify all possible land parcels and select from them the most suitable parcels based on specific criteria.

The criteria for a suitable site are

It is preferable that the costs be reduced by requiring the site to be

Create the database

Much of the required data is available. Each criteria will require a data layer.

Plan analysis

The project analysis will consist of the following phases

Assembling the database

Copy the project folder

Create an ArcCatalog connection to the folder

Create the WaterProject geodatabase

Create a City_layers and an Analysis folder

Add data

Copy parks feature class to WaterProject

Use ArcCatalog to copy the parks feature class of the parks feature dataset of the Greenvalley database to the WaterProject database.

The actual data is copied to the WaterProject database since it is already part of a database rather than a layer.

Create streets and flood zone layers

These layers will not be modified so layers will be created as shortcuts to the data. From the Greenvalley database, select the Transportation feature class dataset. Select the street_arc feature class and click Create Layer. Save the layer as "streets" in the City_layers folder. The data for this layer is in the Greenvalley database.

Create a flood_zone layer from the Hydrology dataset and the flood_polygon feature class.

Preview the data in ArcCatalog

Create a map in ArcMap

Add the layers from the city data

Data may be added from the toolbar/menu or by dragging from ArcCatalog. Add the 2 parcel shapefiles from the City_share folder. Add the flood_zone and streets layers from the City_layers folder. Add the junction coverage from the utility folder in the City_share folder. Add the parks_polygon feature from the WaterProject geodatabase.

NOTE: The addition of some datasets may generate a warning message indicating the data is not in the same coordinate system as the base map. The software should be able to do the necessary conversions.

The elevation data (raster data in a grid file) and the lowlands shapefile should be added from the state provided data. There is a problem with the lowlands layer - it does not appear because it is in an unknown coordinate system.

Create a new layer from the elevation grid file. Edit the properties of the elevation grid to modify the Symbology to use an orange to blue color ramp, invert the color ramp and set the display transparency to 50%.

Data preparation

Define coordinate system for elevation data

The coordinate system for the elevation grid is defined, but there is no coordinate system defined for the lowlands shape file. In ArcCatalog, view the coordinate system for the parks_polygon file by viewing the Spatial tab of the Metadata selection. This file uses a transverse Mercator projection. Note that the coordinate system used for the elevation grid is a Lambert azimuthal equal area projection. ArcMap translated this coordinate system so the elevation grid could be displayed. There is a file named state_dot.prj that defines the coordinate system used for the lowland shapefile. View the properties of the original lowlands.shp file to see that the spatial reference value of the shape field is "unknown". Select the state_dot.prj file as the coordinate system.

Digitize an historic park

There is a new historic park that is not included in the park_polygon file. A scanned image of the boundary of the park is available. This image can be digitized and added to the parks feature class.

Save the current map and open a new map. Four data sets will be added to this map: the existing parks feature class, the scanned image of the new park boundary (TIFF image), the streets layer to be used for registering the image, and the parcel_2 coverage to be used to "snap" the park boundary since it aligns with a parcel boundary. Add the 3 layers to the map. Add the image to the map - there will be a warning message since there is no defined geographic coordinate systems for the image - it is defined in inches (scanner units).

Select the historic image and use zoom to layer to view the file.

The park image has registration marks at certain street intersections. The image can be registered by adding links between these marks and the street layer. Open an overview window to make the registration process easier.

Find the park area on the streets layer by using find to locate one of the streets on the image. When the street name is found, select zoom to features. Enable label features for the street layer. Zoom to the region of the park. Turn off the display of parcel_2 to make the map easier to read.

Register (georeference) the image by creating at least three links between the image and the street layer. Display the Georeferencing toolbar and select the historic.tif layer in it. Select fit to display.

Select add control points from the georeferencing toolbar and, using a magnifier window, center the magnifier window over the registration mark (602). Repeat for 601 and 473 and select "update georeferencing" from the toolbar.

For the parcel_2 layer, set the fill color to "no color" and the outline color to red. Uncheck the streets layer so it will not display. Zoom to the area of the historic park. Add a bookmark from the view menu.

To begin the digitizing process, open the editor toolbar and select start editing. Be sure the parks_polygon layer is selected to be edited and the task is create new feature.

Set the snapping environment to align the new park boundary with existing parcel boundaries. Click editor and then click snapping. Check the box in the vertex column for the parcel_2 layer to snap the editing cursor to the vertices of the parcels. Click the create new feature tool to begin adding points.

It is possible to use the pan and zoom tools as you digitize. The magnifier window may also be used. Click to add points beginning with the NE corner and select finish sketch when complete.

Click the attributes button in the edior toolbar, change the name of the feature to "Homestead Historic" and select save edits. Remove historic.tif from the map.

Merge the parcel layers

Zoom to layer for parcel_2. Add parcel_1 to the map. Select the Geoprocessing wizard from the tools menu and choose merge layers. Set the output to be "parcel01mrg" in the Analysis folder and save the layer. Remove the parcel_1 and parcel_2 layers.

Save this map as WasteWaterProject.

Performing the analysis

Find parcels within the acceptable area

The approach is to find those areas that are within 1,000 m of the river and within the lowlands area.

1. Buffer the river

Add the river layer to the map. For ease of viewing, turn off display of parcels and zoom to full extent. Select the Buffer Wizard from the Tools menu. Create a buffer 1,000 meters around the river. Choose the dissolve barriers option since the river is composed of multiple line segments. Save the buffer layer in the Analysis folder.

2.Intersect with the lowland area

Add the lowland shapefile to the map and use the Geoprocessing Wizard to intersect the river_buffer and lowland areas. Save the result as low_river in the Analysis folder.

Find parcels outside the unacceptable areas

1.Buffer the parks

Use the Buffer Wizard to create a buffer layer around the parks. The buffer should be at a distance of 150 m. Dissolve the barriers but create buffers only outside the polygons. Save the shapefile in the Analysis folder.

2.Buffer the residential parcels

To buffer the residential parcels, the subset of parcels that are coded as residential must be selected. The metadata for the parcel layer indicates that a Landuse code of 510 represents a residential parcel.

Zoom to the parcel layer. Choose Select By Attributes from the Selection menu. Create and apply the "LANDUSE = 510" query.

Create a buffer of 150 m around the selected parcels using the Buffer Wizard. Select Clear Selected Features from the Selection menu.

3.Overlay the park and residential buffers.

Use the Geoprocessing Wizard to take the union of the park buffer and residential buffer layers. Save the result in Analysis as respark_buffer.

4.Overlay the flood zone layer.

Use the Geoprocessing Wizard to form the union of the respark_buffer and the flood zone. Save the result as res_park_flood in Analysis.

Find parcels meeting location criteria

The acceptable parcels are those outside the res_park_flood polygons but inside the low_river polygons.

1.Select parcels outside res_park_flood

2.Select parcels within the river and lowlands buffer

3.Select vacant parcels from the current selection

The metadata indicates that vacant parcels may have any Landuse code from 700 through 799. Use Select By Attributes to select from the current selection in parcel01mrg. Construct the query "LANDUSE >= 700 AND LANDUSE <= 799".

4.Export the selected parcels

Right-click parcel01mrg and choose Export Data under Data. Save the data as parcel_sel in Analysis. Add the layer to the map and Clear Selected Features.

Find the "best" parcels

By selecting those parcels within 50 m of a road and within 500 and 1,000 m of the main wastewater junction, the acceptable parcels can be color-coded on the final map.

1.Add data fields to parcel_sel

Right-click parcel_sel to Open Attribute Table. Select Add Field from Options to add a field named ROAD_DIST of type Short Integer. Add a field named JUNC_DIST.

2.Select and label parcels within 50 m of a road

Display the streets layer amd use Select by Location to "select features from" parcel_sel that are within a distance of 50 m from features in streets. The selected parcels are highlighted in the attribute table. Choose Start Editing from the Editor toolbar. Right click the ROAD_DIST field and select Calculate Values. Type "50" in the expression box. All selected parcels now have the value 50 in the ROAD_DIST field.

3.Select and label parcels with 500 and 1,000 m of the main wastewater junction

Add the wastewater junction to the map and use the Buffer Wizard to create a multiple ring buffer around the wastewater junction. Save the layer as Analysis\junction_buf. Use Select Features to select the 500 to 1,000 m buffer by clicking in it. Then use Select By Location to select the parcels that have their center in the selected features of junction_buf. Use the editor toolbar to edit parcel_sel and assign the value 1000 to the JUNC_DIST field of the selected parcels. Repeat this process to assign the value 500 to the appropriate parcels.

4.Find parcels that are large enough

Since there is no single parcel large enough in the suitable area, a group of parcels must be selected. Using Select Feature various groups can be selected. The Statistics option found by right-clicking on the Area column of the attribute table will display the sum of the areas of the selected parcels. A group of foour parcels immediately west of the wastewater junction are large enough.

It is also possible to investigate parcels that are large enough to determine why they are not acceptable. For example, use Select By Attributes to find all parcels with an area of at least 150,000 square meters. It might be useful to explain why any such parcels are not acceptable. Two of these parcels have no Landuse code. It is possible they are vacant but have not been coded as such. These two largest parcels, however, can be seen to be in the flood plain. The third largest parcel, which is vacant, lies mostly outside the river buffer - it is deemed to be too far from the river. However, it might still be a good site since it is a single parcel of land and is barely outside of the required distance.

Create a layer containing this alternate site by by selecting the parcel and using the Create Layer From Selected Features option for the parcel01mrg layer.

Designing the map

A map should be prepared for presentation to the City Council and the public. The map should contain three maps on one page.