GIS2: Geo-processing and Metadata

Treg Christopher

Three Views of a GIS

• The Map View

• The Database View

• The Model View

Three Views of a GIS

• The Model View: – A GIS is a set of information

transformation tools (i.e. geoprocessing) that derive new data from existing data.

• What are the three types of vector data?

Geoprocessing using Vector Data

•Points, Lines, Polygons

Vector Data – Overlay Analysis• Union

– Spatial features and their attributes are joined to create a new layer

Vector Data – Overlay Analysis• Intersect

– Only the features that are common to both layers are combined to create a new layer

• Identity

Vector Data – Overlay Analysis

• Erase– Remove an areas from

the larger, geographic area

– Example: Where are endangered nesting areas where human activities aren’t allowed?

Proximity Analysis :Nearest Neighbor

Vector Data – Proximity Analysis

• Buffer:– find features contained

inside or that fall outside the specified distance.

– Points, lines, or polygons

– Different buffer distances

– Multiple bands

– Overlapped or dissolved zones

Proximity Analysis :Variable Width Buffering

Width of buffer varies by attribute value

Example: a buffer based on stream type and Timber BMP

Ephemeral - small or no buffer

Intermittent- 30ft

Perrenial-150ft

Vector Data – Feature Extraction

• Clip– Includes only those features

of the input theme that are within the areal extent of the clip theme.

– Isolate a particular area of interest.

– For aesthetics, storage space and processing time

– Input layer be point, line, or polygon features, but the clippinglayer (i.e., "cookie cutter") must be a polygon layer.

• Dissolve– Removes boundaries between

polygons that have the same value of a selected attribute.

– Reduces processing time, visual clutter, storage space

• Append– Add tiles together to create

one layer– Large datasets are often tiled

• Soils (by County)• Topos (by 7.5minute Quad)

Other geoprocesses

Geo-processing use Raster Data

• Square cells of equal size • Raster (grid) is well suited for computing

because: (1) grid cell have fixed locations, and• (2) grid can be treated as a two-dimensional

array;

Number of columns

Num

ber

of

colu

mns

Cell size

Examples? DEM, Satellite Imagery, Aerial Photo

Raster Data AnalysisMap Algebra

• Local Operation

Single grid

Raster Data Analysis Map Algebra

• Zonal Operation

Zonal Mean Example - Map Algebra

3333

3311

221 1

2211

Zone Grid

4431

6732

154 1

1221

Target Grid

4.174.174.174.17

4.174.172.172.17

2.252.252.172.17

2.252.252.172.17

Result

Three Views of a GIS

• The Database View: – A GIS is a unique kind of database of the world—a

geographic database (geodatabase). It is an "Information System” for Geography.

• Spatial Data

• Attribute Data

• Metadata

What is Metadata?• 1. What does the data describe?

– What is geographic area of the data?

– When was it collected?– what are the units of measure?

• 2. How reliable is the info?– How was the data generated,

processed, and modified? • 3. Who produced the data? What is the data

type?

• 4. What is the projection?• 5. What does each value in each

field of the table mean?• 6. How can I get it? Usage restrictions?• 7. Who wrote the metadata?

Example of Metadata at: http://www.vcgi.org/

Steps in GIS for Your Project

• Identifying the goals of the project

• Identifying the questions

• Choose the data

• Choose the tools to analyze the data

• Conduct the analysis and generate results

Example: Finding sites for creating new campground areas

• The goal– Find public places in Chittenden County that are suitable for low-level

development as campgrounds.• The questions

– What are environmental concerns for this development?• Water quality• Damage to vegetation

– What makes a campground suitable to the user?• Microclimate• Proximity

• The data– Environmental concerns

• Hydrology (streams, lakes), Wetlands, Areas of threatened species– Human concerns

• Slope, Aspect, Roads, Trails

The Tools

• Confine to Project Areas (Clip)

• Proximity to Features (Buffer)

• Remove Buffered Areas (Erase)

• Find areas of low slopes (Intersect)

ArcIMS Viewer for Chittenden

• Website at:

• http://ecovalue.uvm.edu/ArcIMS/Website/chittenden

End

• Questions?

Review Questions

• Geo-processing is a part of which of the 3 views of a GIS?• List and describe 4 types of overlay analyses• Be able to describe real life examples in which you would

use these• Describe “buffering” and give an example of it’s use • Describe “clipping” and give an example of it’s use• Be able to distinguish between examples of zonal, raster

processing and cell-by-cell, raster processing• What is metadata?• List and describe 4 of 7 elements of metadata