GISP 6: Analytical Methods Questions and Answers 100% Pass

GISP 6: Analytical Methods Questions and Answers 100% Pass What are the ways you can SELECT features based on ATTRIBUTE? -New Selection -Add to Selection -Remove from Selection -Subset Selection -Switch Selection -Clear Selection Semivariogram a model of the variance between points and their distance apart What is map algebra? set of primitive operations that allows two or more raster layers of similar dimensions to produce a new raster layer using algebraic operations such as addition, subtraction etc. What is Classification? process of representing members of a group by the same symbol, usually defined in a legend What is the one of the most basic questions asked of a GIS? "what's on top of what?" e.g. What landuse is on top of what soil type? e.g. What parcels are within the 100-year floodplain? e.g. What roads are within what counties? What are the methods of spatial selection involving CONTAIN? -Contains - features contain an input polygon -Completely contains - features must be completely in an input polygon -Contains Clementini - features must be completely in the input polygon but if it's on the boundary, it will not be selected -Contained by - Same as within What are the four classes of map algebra transformations? -local -focal -global -zonal What are the two methods for performing overlay analysis? —feature overlay (overlaying points, lines, or polygons) -raster overlay What is the most basic use of classification in GIS, cartography and remote sensing? Generalize complexity in and extract meaning from geospatial data. Range The distance on a semivariogram where the model first flattens out What are the three basic methods of spatial selection? -Intersect -Within a distance -Are Identical To - features are identical to input layer How do LOCAL OPERATIONS work in the context of map algebra transformations? -work on individual pixels -combine rasters that overlay each other -e.g. add/subtract/etc. cells that are in same location What are the basic steps to overlay analysis methodology (based on Boolean logic)? a. Define problem b. Break problem into submodels c. Determine significant layers (and if some of these layers need to be created) d. Reclassify or transform data within a layer (e.g. union) What is a classification schema (or key)? Set of criteria based on feature's attributes used to decide which individuals go into each class Sill The value that the semivariogram model attains at the range (on the y-axis) What is Spatial Overlay? -superimposing layers of geographic data that cover the same area to study the relationship between them Nugget Theoretically, at zero separation distance (lag = 0), the semivariogram value is zero. However, at an infinitesimally small separation distance, the semivariogram often exhibits some value greater than zero. For example, if the semivariogram model intercepts the y-axis at 2, then the nugget is 2. How do FOCAL OPERATIONS work in the context of map algebra transformations? -work on cells and their neighbors - calculates a value based on all neighboring cells -e.g. find average of all cells around a certain cell What is meant by: "good categories should have minimal intra-category variation and maximal inter-category variation" Ideal categories contain things that share many characteristics with other members of the category, and have little in common with things outside the category. What are the methods of spatial selection involving WITHIN? -Within - features will be selected if inside a selecting polygon -Completely within - features will be selected if completely within selecting polygon (no overlap) -Within Clementini - features will be selected and cannot be entirely on the boundary of the features -Have their Center In - Features will be selected if their center falls within a selecting feature What are the methods of spatial selection involving TOUCHING/CROSSING? -Boundary Touches - features will be selected if they have a boundary that touches a selecting features (must be completely inside or outside the polygon) -Share a Line Segment With - features selected if they share a line segment -Crossed by the Outline of - Input features will be selected if they are crossed by outline of a selecting feature How do GLOBAL OPERATIONS work in the context of map algebra transformations? -work on the entire layer - apply a formula to all cells -e.g. Add/subtract/multiply/etc. all cells based on one value -e.g. Find the distance from one cell to all cells What is Overlay? -two or more maps or layers are superimposed for showing relationships between features Define mutually exclusive in the context of classification -there is no overlap between any two categories (ideally) -an individual cannot belong to two categories simultaneously Partial sill Sill minus the nugget in a semivariogram Kriging -Tool in 3D analyst -Multistep process 1. exploratory statistical analysis of the data 2. Variogram modeling 3. Creating the surface, and 4. (optionally) exploring a variance surface. -Most appropriate when you know there is a spatially correlated distance or directional bias in the data. Define collectively exhaustive in the context of classification -categories "exhaust" or include all individuals (ideally) -an individual cannot belong to zero categories What are the main Vector Overlay Tools? -Identity -Intersect -Symmetrical Difference -Union -Update What is the most commonly used DML command? SELECT How do ZONAL OPERATIONS work in the context of map algebra transformations? -work on areas of cells that share the same value - computing a value based on cells in a particular zone e.g. a watershed How would you word a query to return all the elements of all the rows of a table called "T"? SELECT * from T; Why is map algebra important to GIS? Major GIS systems (including ERDAS Imagine and ArcGIS) use map algebra concepts What is the output of the IDENTITY tool in the context of Vector Overlay Tools? Input features, split by overlay features What is the classification method used for choropleth and isarithmic maps? -Quantitative Thresholding -Dividing the range of values of a single quantitative attribute into ordinal classes Semivariance Degree of distance between points on a surface What is the EQUAL INTERVAL method of Quantitative Thresholding? -arranges a set of attribute values into groups that contain an equal range of values. -take the range of your data (maximum - minimum) and divide by your chosen number of categories. What are Descriptive Statistics? - discipline of quantitatively describing main features of a collection of information -e.g. Summarizes a sample to learn about population What is the output of the INTERSECT tool in the context of Vector Overlay Tools? Only features common to all input layers How would you word a query to return all the elements from column C1 in a table called "T"? SELECT C1 from T; How does ArcGIS 10 implement Map Algebra? in Python How would you word a query to result in all the elements of all the rows where the value of column C1 is '1' in a table called "T"? SELECT * from T where C1 = 1; What is the output of the SYMMETRICAL DIFFERENCE tool in the context of Vector Overlay Tools? Features common to either input layer or overlay, layer but not both What are the pros and cons of the EQUAL INTERVAL method of Quantitative Thresholding? Pro: help show different groups when they are close in size. Con: this pattern doesn't often occur in geographic phenomena How are descriptive statistics distinguished from inferential statistics (or inductive statistics)? -descriptive statistics aims to summarize a sample -inferential (inductive) statistics aim to use data to learn about population that sample is thought to represent. How would you word a query to result in every combination of rows in from two tables called "T1" and "T2"? SELECT * FROM T1, T2; will result in every combination of T1 and T2 rows e.g., if T1 has 3 rows and T2 has 5 rows, then 15 rows will result What is the output of the UNION tool in the context of Vector Overlay Tools? All input features What is the QUANTILE method of Quantitative Thresholding? -divides the attribute values equally into a predefined number of classes. -attribute values are added up, then divided into the predetermined number of classes. -take the number of total observations and divide that by the number of classes resulting in the number of observations in each class. What are Summary statistics? -statistics used to summarize a set of observations to communicate largest amount of information as simply as possible -e.g. arithmetic mean -e.g. standard mean absolute deviation -e.g. correlation coefficient What is the Coefficient of Determination? -denoted R2 or r2 -pronounced "R squared" -proportion of variance in dependent variable that is predictable from independent variable -i.e. number that indicates how well data fit a statistical model Describe the JOIN spatial data selection function combines two attribute tables into one using a common key between tables What are the benefits of the QUANTILE method of Quantitative Thresholding? -classes are easy to compute -each class is equally represented on the map. -ordinal data can be easily classified b/c the class assignment of quantiles is based on ranked data What is the output of the UPDATE tool in the context of Vector Overlay Tools? Input feature geometry replaced by update layer Describe the MERGE spatial data selection function combines multiple input datasets of the same data type into a single new output Which Vector Overlay Tools are used for binary overlay? -Identity -Symmetrical Difference -Update Visually, how is the Coefficient of Determination represented? Fit to a line or curve What is the benefit of the JENKS NATURAL BREAKS method of Quantitative Thresholding? -reduces variance within classes and maximizes variance between classes. Describe the APPEND spatial data selection function combines datasets of same data type into an existing dataset Which Vector Overlay Tools are used for multiple layer overlay? -Intersect -Union What do a 0 and a 1 Coefficient of Determination mean? - 1 indicates the line fits perfectly with the data -0 indicates the line does not fit at all (data is random) When would a Coefficient of Determination outside the range 0 to 1 occur? -when model fits data worse than a horizontal hyperplane. -e.g. when wrong model was chosen -e.g. nonsensical constraints were applied by mistake. Describe the UNION spatial data selection function combines input features with another feature dataset What is the JENKS NATURAL BREAKS method of Quantitative Thresholding? - aka Optimization -designed to optimize the arrangement of a set of values into "natural" classes. -minimize the average deviation from the class mean while maximizing the deviation from the means of the other groups. Which Vector Overlay Tools can use any input data type? -Identity -Intersect -Update Which Vector Overlay Tools must use polygons as input data? -Symmetrical Difference -Union What is the GEOMETRIC INTERVAL method of Quantitative Thresholding? -used for visualizing continuous data that is not distributed normally. -designed to work on data that contains excessive duplicate values, e.g., 35% of the features have the same value. Describe the CLIP spatial data selection function extracts input features that overlay the clip features (keeps inputs attributes) Describe the INTERSECT spatial data selection function extracts features which overlap in all layers to new feature class (joins attribute tables) Which Vector Overlay Tools must use polygons as overlay data? -Identity -Symmetrical Difference -Update What is the STANDARD DEVIATION method of Quantitative Thresholding? -finds the mean value of the observations -then places class breaks above and below the mean at intervals of either .25, .5, or 1 standard deviation until all the data values are contained within the classes. -shows how much the feature's attribute value varies from the mean. What are the main Raster Overlay Tools? -Zonal Statistics -Combine - Single Output Map Algebra - Weighted Overlay -Weighted Sum What is the best way to symbolize features when using the Standard Deviation method of Quantitative Thresholding? -Use a diverging color scheme twill emphasize which observations are above and below the mean What does the COMBINE Raster Overlay Tool do? -Assigns a value to each cell in output layer based on unique cominations of values from several input layers. What are the maximum and recommended number of classes to use when categorizing geospatial data? Maximum: up to 7 classes Recommended: 5 What does the ZONAL STATISTICS Raster Overlay Tool do? -Summarizes values in a raster layer by zones (categories) in another layer -e.g. calculate the mean elevation for each vegetation category What are the implications of using different classification styles? each style will highlight different aspects of the trends in the dataset What does the SINGLE OUTPUT MAP ALGEBRA Raster Overlay Tool do? - Lets you combine multiple raster layers using an expression you enter —e.g. you can add several ranked layers to create an overall ranking What is the danger of choosing the wrong classification methodology? could cause the data to hide important information or misinform the reader What does the WEIGHTED OVERLAY Raster Overlay Tool do? - Automates the raster overlay process and lets you assign weights to each layer before adding -can also specify equal influence to create an unweighted overlay What does the WEIGHTED SUM Raster Overlay Tool do? - Overlays several rasters multiplying each by their given weight and summing them together.