GIS Exam 2

Interpolation

• A procedure of estimating the value of properties at un-sampled sites within the area covered by existing point observations

• How?

  • Performed by fitting some plausible model of variation to the values at the known points and then predicting the values at unknown locations

Definition of a GIS

A system of computer hardware, software, and people used for entering, storing, manipulating, analyzing, and displaying geographic or spatial data

Extrapolation

Estimating the value of a characteristic/property at sites outside the area covered by existing observations

Spatial Scope

The area covered by spatial operations

List the three spatial scopes used in spacial analysis

1. Local Operations

2. Neighborhood Operations (most important for raster)

3. Global Operations

Provide a full and complete definition of a buffer used in GIS. Include an example drawing of a buffer in your explanation and refer to the drawing

a polygon of proximity that is built around an area

Provide a real life specific application/scenario of when you would use a buffer in your GIS analysis

If I was in charge or protecting an endangered plant species, I would utilize buffers to create a protection layer around their habitat. This would prevent any disturbances to the area and anywhere within a close proximity to the endangered plant species.

Given the successful recoding in question 6 above, what is the next step in the analysis process you should perform

I would perform a dissolve

List three major categories of models used in GIS

1. Cartographic Model

2. Spatio-Temporal Model

3. Network analysis

I am interested in studying the long-tailed snipe survival rates for the Wagon Hill Park area of Durham, NH over the last 3 years. I need a detailed analysis of what is happening to the snipes and why. Should I use trend surface analysis here (Yes or No) and why?

No, it would not be a good idea to use trend surface analysis, as wagon hill is a relatively small area and 3 years is quite a short time span.

Trend Surface Analysis

to find general tendencies of the sample data, rather than to model a surface precisely

I am interested in studying the long-tail snipe survival rates in New England over the last 50 years. I need to evaluate if the snipe population is shrinking or expanding. Should I use trend surface analysis here (Yes or No) and why?

Yes, trend surface analysis would be applicable in this case. This is because New England is a much larger area and the data set is greater (ie. more time). This means there would be enough data to be displayed in a trend surface analysis.

Of the many we discussed in class, list, with an explanation if necessary, 4 possible sources of error in a GIS data layer? You must be specific.

1. Age of Relevance

2. Positional Accuracy

3. Classification of the data layer

4. Quality of the data layer

What is spatial autocorrelation? (provide a clear and complete definition)

Spatial autocorrelation is the presence, absence, or feature that directly impacts the same presence, absence, or feature of a neighboring attribute.

Provide an example of spatial autocorrelation that clearly demonstrates your understanding of the concept?

If someone in class was eating a slice of pizza at the front of the room, the person in the front row would be able to smell it and then crave pizza. In contrast, the person sitting in the back row would not be able to smell the pizza, therefore not craving it.

What potential pesky problem typically results from having a common feature such as water or roads in two or more input layers of an overlay analysis?

Slivers in Data

What method must you employ to solve this problem on flash card 14?

Conflation layer

What is the purpose of the Core Area Mapping spatial analysis technique?

After providing the purpose, please provide a real-world example of when this technique should be used.

Core area mapping is used to identify area features or polygons from a set of points and lines. Ie. Wildlife habitat or home range

Define accuracy and precision. You must use words and pictures to clearly explain these 2 important concepts.

Accuracy is how close something is to the desired target.

Precision is the consistency of the attempts

The calculation of root mean square error (RMSE) involves squaring all the errors, then summing them up, and then taking the square root of this total. Please explain why it is not appropriate to simply add up the errors instead of having to square

It is not appropriate to add up the errors instead of having to square because the value would come out to zero. This would indicate no errors, therefore it would not be accurate and it is better to square them, then take the square root.

What measure/technique is used to assess positional accuracy?

RMSE

What measure/technique is used to assess thematic/attribute accuracy?

Error Matrix

I am interested in identifying an area to create a new Fun Zone Park including mini-golf, go carts, batting cages, etc. for the town of Stratham, NH and have determined the following general criteria for performing a cartographic modeling analysis to pick the best location. Please provide the appropriate GIS data layer that you would get from GRANIT and then the refined (or GIS specific) criteria for each of the general criteria.

DEM

Digital Elevation Model

What does a DEM provide

a digital representation of a portion of the earth's terrain over a two dimensional surface

Triangulated Irregular Network

A surface representation derived from irregularly spaced sample points and break-line features. The TIN data set includes topological relationships between points and their proximal triangles. 

Interferometry

 The study of interference patterns created by combination of two sets of radar signals

• Reflected light is received by an antenna and recorded by digital computer

3 aspects of Topographic Analysis

1. elevation

2. slope

3. aspect

Aspect

▪ Direction of the slope

• Reported as azimuth angle, measured clockwise from North

VIEWSHED ANALYSIS or Hide the Clearcut

A very common and powerful technique for hiding or showing things

what 3 GIS data layers does hide the clear cut use?

• Elevation 

• Surface feature locations 

• View points

GNSS

Global Navigation Satellite System 

Why use a GNSS?

• Mapping 

• Navigation 

• Decision support tool

Who uses GNSS?

• Government agencies 

• Researchers 

• Businesses 

• Consumers 

• Really everyone

Who developed GPS?

 US Dept of Defense in 1978 

How does a GNSS Receiver determine its position?

• By measuring distances from satellites 

What is Trilateration? 

• If you know the distances of three known points, you can determine your position 

How do receivers measure distances? 

• Distances are determined by signal travel time 

  • Signal travels at speed of light 

• 4 minimum satellites are needed 

  • Required to help minimize eros caused by inaccurate clock in the receiver 

A receiver will display a position, but: 

• Position has error 

• Varies because of error 

• 95% of the time accurate position of receiver 

What can we control for a reciever?

• Geometry of satellites 

• multi path 

• Atmospheric delay 

PDOP

- Position Dilution of Precision 

Multipath

Satellite signal is reflected before reaching receiver - avoid proximity to solid objects 

Atmospheric Delay

set receiver mask angle to 15 degrees

How does differential correction help? 

• Eliminate or reduces numerous errors 

• Corrections improve accuracy of position