Sketching, Evaluating and Visualizing Development Scenarios in a Geodatabase
It seems that most of what we do with GIS is to explore and evaluate existing conditions. Yet, once we learn to create and alter GIS data, there is no reason we can't create alternative future scenarios, and evaluate them with the same modeling techniques that we have used with data that supposedly represents some current state.
- Think about what we need to represent, and create a data model to hold our representations.
- Create representations of new roads, buildings and of altered land use of our scenario
- Evaluate the impacts of our development proposal.
- Create a visualization of your scenario in its context in 3d
Specific Techniques and User-Guide References:
During the performance of this tutorial we will discuss several techniques that you will want to explore in the software user manuals later. The text of this tutorial will also provide references to specific top[ics from ArcMap's on-line help. These references are highlighted like this.
- Building a Geodatabase Chapter 2 and Chapter 5
- Editing Shape Features and Attributes: Editing in ArcMap Topics from Chapters 3, 6 and 9
- Visualizing Scenarios in Three Dimensions: Using ArcGIS 3D Analyst, Using 3D Analayst Chapter 12
To download the tutorial data set Right-click here
Exploring our Data Model
We want to build and evaluate several development scenarios that will require specific alterations to the land-cover of a site, building of new roads, addition of buildings that have different uses and capacities, and different planting schemes. We would our representation to avail itself easily to analysis, comparison with other alternatives, and evaluation.
Before we begin building our individual scenarios, we should work with our colleagues to decide the critical components that we will want to analyze and compare, and how we will represent them in the computer. You can think of this as building a formal dictionary of the nouns that we will have at our disposal. In the world of information systems, this stage is known as Creating a Data Model.
Our data model has been coded into a geodtabase which has feature-classes prepared to hold representations of Trees, Buildings, Land_Cover changes, and our Site Boundary All of these feature-classes reside within a feature dataset named Scenario which has been endowed with a spatial extent and spatial reference from the Massachusetts layer in our base data folder. The geodatabase also has a set of controlled domains that determine what values can be entered into certain columns. You can see these by clicking properties for the geodatabase itself.
Create a Scenario
Creating a scenario involves making a copy of the template scenario, and then populating the shape files with our proposed site interventions. For this, we should be sure to open and consult the Editing in ArcMap user guide.
Make a new Scenario Instance
- Make a copy of the template scenario and rename it to indicate a name for your development scenario (e.g. 'scenario1')
- Open the map file in your copy of the template scenario folder. The map file opens up our empty feature classes and several layers from our base_data and model_results folders.
We will begin by finding an apropriate site. For this, we may want to consult some of the siyte systems models that we made earlier in our cartographic modeling exercise. We can find areas that are more likely to be warm in winter and cool in summer and where it is likely to be legal to build. Once we find such a site, we can begin to create a development proposal.
Creating a proposal is a simple process of populating our empty tables. We will begin by making a simple poygon for our site boundary.
Beginnig to Edit
- Use the ArcMap on-line help index to find the heading Editing -> features
which means -- type editing, in the index search field, and then look down the list
of subheadings until you find 'Features'.
- Now, if you don't remember what we did in lab, then read the section of the
page that begins with 'An Overview of the Editing Process.' Also read the section
'Exploring the Edittor Toolbar'
- We are about to add a polygon that defines the boundary of your site. Before
we do this, it will be interesting to open the attribute table for your site
layer. It should have no rows in it at this point.
- Now set 'Site' as your target layer and 'Create New Feature' as your editing task
and create a polygon over the area where you intend to build.
- Now you see your site layer now has a record! If you want to you can update
the Name field.
More complicated Editing Tasks
OK, so now you know how to start editng and to make a simple polygon. Next we will try some more complicated edinint procedures. We will make a prototype building of a specific size, then update its attributes, and then use copy, paste and the rotate tool to make several copies of this building. One problem that comes up when trying to edit when there are lots of layers open, is controling what is selected when you click somewhere. This can be confusing, because when we are zoomed into the small buildings, we may accidentally select, copy and paste the site polygon, which, can be very confusing and annoying. This is why we will begin by making our buildings layer the only layer that is selected.
- Use Selection->Set Selectable Layers to make your buildings layer the only one that is selectable.
- Set your buildings layer as your editing target
- click one vertex
- We want to make a building that is exactly 4 meters by three meters since we don't know exactly where to click the next vertex, put your mouse somewhere near the right direction, then right-click. You will see among the options in this context menu, Delta XY
- Select Delta XY and enter 4 in the first(dx) field and 0 in the second field. You have just added a vertex 4 meters to the east of your first one, and zero meters to the north!
- You may have to zoom in now to see what is going on. You can grab the zoom tool, even though you are in the middle of editing a polygon, and zoom in to get a good view of your little cabin.
- Now when you grab the pencil tool fromthe editor toolbar, you will resume editing your building.
- Now to enter the final wto vertices of your 3x4 cabin, use the DeltaXY tool to enter the next vertex at 0,-3 and -4,0.
- Now right-click onecr more and choose Finish Sketch to end your sketch
- Finally, lets update the attributes of this building, as follows:
- Stories = 1
- Use = "Residential"
Copying and Pasting Buildings
- Find the Edit Tool on the editor toolbar. If you roll over the tools slowly, their tool-tips will show up...
- Use the edit tool to pick your building.
- Now you can make a copy of the building by choosing Edit->Copy or by simply by holding down your Ctrl key and pressing the c key.
- You can nlow paste a copy on top of the original, by pressing Ctrl-v. since the new copy is exactly on top of the old one, you can't see it.
- Now use the edit tool to pick your building and you can drag the copy off to another location.
- Fianlly, you can rotate selected buildings with the Rotate tool at the right-hand end of the editor toolbar.
- Finally, take a look at the attribute table and see that the attributes of your selected building have been propogated with their shapes!
Now with these techniques, you can see how you can create anything you need to in order to represent any aspect of your site. After you finish this tutorial, you may want to add some roads and some polygons to represent the various alterations you may make to the landcover, such as pavement, clearings, and lawns.
Make another prototype and some copies
- Now to make things interesting, create a prototype of a larger, commercial building -- such as a large building footprint, which will have its stories attribute set to "2" and its use set to "Commercial".
- Copy and paste some copies of this building
Create some Trees and Areas of New Land Use
- Create some areas of altered land cover on your New Land Cover layer. Be sure to update the Cover attribute of each new polygon you create.
- Create some roads, and update their Width> attribute. Roads may be 10 or 8 meters wide.
- Create some trees and update their Type attribute.
Now for the moment we've been waiting for -- to use our sketch of buildings to create a summary of the impacts and capacities of your site development scenario. We have added several buildings of different types and sizes, and we have proposed to change some of the existing land-cover. But how much, exactly? The benefit of making our sketch in a data model is that we may now systematically extract information from our sketch that could help us compare one scenario with another.
This procedure is accomplished with a series of processes that has been saved with our template (and therefore copied with our scenario.) To retrieve, explore and run these processes, we should start by loading the Evaluation toolbox and open the model inside.
Add and Explore our Evaluation Model
- Add your toolbox panel by pushing the red toolbox icon on your arcgis toolbar.
- If your Evaluation toolbox isn't already there, right-click in the toolbox panel and add the toolbox from your copy of the scenario folder.
- Right-click on the model inside your evaluation folder and choose 'Edit'.
- The yellow boxes in this model are the processes that we will use to create the summary of Gross Floor Area per each programmed use, and the amount of land that switches from one use to another. Open each of these boxes and take a look at the help for each one to see what they do.
- Starting from left to right, top to bottom, run each of the processes in your model.
- The summary of your building-programs will be a table named Building_Statistics. YOu will need to set your Table of Contents to Source Mode to see this.
- The new raster named Combined> The attribute table for this grid provides a report of the new land uses in a grid of 10x10 meter cells, and what the values for these cells was on the original land use layer. The Count column reflects the number of each cells for each combination of old/new uses. Because the cells are 100 square meters apiece, you can divide the count by 10 to get hectares. The land uses represented by the values in this table can be looked up in the Metadata for the MassGIS Land Use Data Layer
Visualizing our Scenario in 3 Dimensions
So all of this seems like a fairly painful wau to make a sketch of a development scenario, and perhaps it is. Kepp in mind that adhering to this system allows us not only to automate the construction of one scenario, but also to systematically compare multiple scenarios, and also to evaluate our proosed future alternatives with the same tools that we have used to evaluate the existing conditions.
Yet another advantage to composing our development scenario this way is that we can visualize our proposal in the context of other GIS data such as areial photos, in three dimensions! To learn more about this you should take a look at Using ArcGIS 3D Analyst,Chapter 12.
Organize an ArcGlobe Project
- Open up ArcGlobe
- add your trees, buildings and site layers form your scenario folder
- add your orthophoto image, 145914.sid from the base_data/massgis folder
- Now, double-click the trees layer, select the Globe Display tab, and uncheck the box next to Rasterize Feature Layer. Then click OK on the layer properties dialog. This important property, and the nnext step are important features of setting up the ArcGlobe display that you should read about in the manual.
- The next thing you will see is a window saying that you must set the View-Distance for your trees layer. This same thing will also show up layer after setting the properties for the buildings. Click OK to set the view distance properties to 'Far'.
Elevating your Aerial Photo
The magic of ArcGlobe is that you can set the ground elevation of various layers to conform with the elevations given by a digital elevation model. We will start with our aerial photo and then do the same with the site layer and the buildings. Finally, we can set the extrusion proprties for the buildings so that they extrude to their story height multiplied by 3 meters per story.
Setting the Base Heights of your Airphoto and Site Layer
- Double-click on your airphoto layer to bring up its layer properties panel.
- Click the Elevation tab.
- Click the button next to Layer floats above globe surface...
- Use the brows button next to this field to find the USGS_DEM in the usge folder of your tutorial dataset's base_data folder.
- Click OK to apply these settings.
- Use the same procedure to set the elevation of your Site layer.
- Read in the ArcGlobe manual in chapter 12, the section on navigating in ArcGlobe. This will explain how you can zoom to your airphoto layer, change your navigate mode to Surface and use the navigate button to rotate your airphoto so that you can see how it has been draped on the digital elevation model.
- You may want to make your site polygon transparent so that you can see your airphoto through it.
Extruding your Buildings
- Your buildings layer should have its elevations set the same way as the layers that you have already set.
- Then under the Globe Exgtrusion Tab you can set the extrusion of your buildings, using the little calculator button, to extrude to their number of stories multiplied by 3 meters per story.
- While you are modifying the building properties, why not set the symbology properties to distinguish the commercial buildings from the residential ones.
- Click OK to see your buildings in 3D!
- If it looks like your buildings are floating above the airphoto surface, experiment with adding a 3 meter offset to the airphoto's elevation properties (at the bottom of the layer's Elevation properties panel.
You can now document your work by exporting images from your ArcGlobe project using FIle->Export Globe