GIS Modeling

GIS Topics and Applications

5 Ms of GIS

•Mapping•Measurement•Monitoring•Modeling•Management

Geoprocessing

• When we perform geoprocessing tasks on our data, we are developing the components of a GIS model.

• We perform geoprocessing every time we:– Use a tool interactively in ArcMap– Use tools from ArcToolbox– Execute commands using the command line– Connect tools in ModelBuilder– Use functions in a script (like Python)

Static and Dynamic

• Static modeling is the series of steps required to achieve some final result.– Available land for development of a nursery– Siting of cell towers

• Dynamic modeling is performed in a similar fashion, but has additional parameters requiring several iterations of the model.– Disease outbreak modeling– Real-time traffic analysis– Spread of wildfires, heavy rain, etc.

Why Model?

• Developing a model for a GIS analysis allows for repeat testing of a hypothesis using different data.

• The model can be coded into a GIS application, so that the steps are performed automatically.

• Easier reproduction of results.• Simplification of workflow.• Informs the computer how to conduct a series of

steps that would be impractical for you to do manually.

Reproducibility

• In performing an analysis, you must have your workflow clearly defined.

• This ensures that you are performing the steps in the correct order using the appropriate tools.

• Missteps are easy, especially when there can be hours of computer processing between steps.

• The GIS model can be exported as a graphic flowchart or a modeling data structure.

Workflow Efficiency

• There are many repetitive steps you will take in your daily workflow.

• Streamlining the process saves you time.• If you always start working in a File Geodatabase

with specific resolution and projection information, a model for generating your specialized GDB can be created.

Human Inefficiency

• You physically cannot perform the steps as fast as GIS can produce the results.

• Certain steps, such as iteration through a feature set would be prohibitively time consuming.– You must perform the same steps 21 times to clip

data to each individual NJ county.– Rail use analysis: 200+ stations

• Minimize the amount of time spent “babysitting” GIS to perform complex analyses.

How do we model?

• ArcGIS has a drag-and-drop interface to ArcToolbox called ModelBuilder allowing you to develop a flow chart of your GIS workflow.– This flowchart is then run step by step to perform

your analysis.• ArcGIS allows for custom scripting that can be

added to ArcToolbox, introducing greater functionality.– Custom export scripts, specialized versions of existing

tools, develop tools not available in ArcToolbox.

ModelBuilder

Introduction to ModelBuilder

• Throughout your GIS education, you've performed several geoprocessing tasks

• We have used geoprocessing tools in sequence to analyze GIS data

• ArcGIS allows you to link tools together to create a workflow

Inside ArcToolbox

Inside ArcToolbox

• Models and Scripts are added to custom toolboxes you create in ArcToolbox.

Model

Script

Toolbox

Toolset

Creating a New Toolbox

• Creating your own Toolbox is not just for organizational purposes. It allows you to share your models with others.

• If you will be sharing your model and using relative addresses, you need to plan the folder location of your New Toolbox carefully.– Default location for a New Toolbox created inside ArcToolbox

is: C:\Users\<user profile>\Application Data\ESRI\ArcToolbox\My Toolboxes.

• Create a new Toolbox by right clicking in ArcCatalog and selecting New Toolbox.

How ModelBuilder Works

• Drag layers you want to participate into the model

• Drag tools you want to use into the model

• Output layers, tables, objects shown in green

• Connect the features using arrows

• Order matters to certain tools (Clip)

Determining Points Within

• Searching for a count by municipality of all the contaminated sites (KCSL) in Gloucester County

• Select just Gloucester County municipalities, then all KCSL within the selected area

• Then perform a spatial join on the two layers to find a count of KCS points within each of the municipalities

Getting Started

• Let's make a new Toolbox to store our models

• Make a new model inside the Toolbox

• Edit the model

Drag and Drop Interface

Order Matters

Order Matters

1

2

Order Matters

1

2

Final Model

Multiple workflows in one Model

reclassed road

distance

non-floodprone layer

residential and wetlands plus buffer

Models used in the

Workplace: N

J DEP

Additional Functionality

• The Model can be expanded further, with more data and tools

• The Model can be exported into a scripting language, allowing for greater modeling capabilities.

Additional Functionality

• Python is the default (and recommended) scripting language for ModelBuilder

• Cursor-based analysis: For each individual feature in a layer, perform some analysis– For each "vacant" polygon, is it surrounded by

environmentally sensitive features?– Count each feature's vertices, rings

• Internet access: automatically download data, then analyze

Going Further

• A ModelBuilder OverviewAvailable on ESRI's support page

• Getting Started Writing Geoprocessing ScriptsAvailable on ESRI's support page

• Dive Into Pythonhttp://www.diveintopython.org/

• Learning Python, 3rd Editionhttp://www.oreilly.com/catalog/9780596513986/