GIS Final
Describe Column, Pie, Area and Scatter graphs
-Column: used to display discrete data using vertical or horizontal bars. This graph compares amounts and can suggests trends in the data. -Pie: Pie graphs emphasize where your data fits in relation to a larger whole and are particularly useful for showing proportions and ratios. This works best with several (three to seven) large categories. -Scatter: This uses data values as x,y coordinates to plot points. The pattern may reveal a relationship between the values plotted on the grid/plane. -Area: graphically quantitative; based on line
Explain the four "edge adjusting" operations we discussed in class. CLIP, UPDATE, SPLIT, ERASE
-Edge adjusting operations only work on one layer of data. Clip: cut out a piece of a coverage using a cookie cutter Update: merge new features using a cut and paste operation Split: splits a coverage into several smaller coverages Erase: removes part of the inside of a coverage
Geostatistics: What are the three types of geostatistical interpolation approaches we presented and reviewed during a lecture in class? Which of these methods allows you to calculate the uncertainty of a predicted attribute value? What is a Prediction Map?
-Inverse Distance Weighted (Deterministic): output type: prediction -Spline (Local Polynomial) (Deterministic): output type: prediction -Kriging (Stochastic): allows you to calculate uncertainty of a predicted attribute value; output type: prediction, standard error, probability, quantile Deterministic interpolators can predict attribute values (Prediction) but do not assess prediction error and cannot create estimates of prediction value uncertainty. Stochastic interpolators can predict attribute values (Prediction) do assess error and can create these estimates of prediction value uncertainty (Standard Error). A prediction map is a map of the outputs of the predicted values from one of the geostatistical interpolation methods.
Briefly describe the three feature classes we can define (point, line and polygon).
-Point: features that are too small to represent as lines or polygons as well as point locations -Line: represent the shape and location of geographic objects too narrow to depict as areas (such as street centerlines or streams) -Polygon: a set of many-sided area features that represent the shape and location of the homogenous feature types such as states, counties, parcels, soil types, and land-use zones
Briefly describe vectorization and rasterization (described in class)
-Vectorization is using vector data to represent fields instead of objects. -Rasterization is using raster data to represent real world objects instead of fields. It is a way to convert polygon, polyline and point feature class data to a raster layer.
Briefly describe the three spatial references needed to make up a coordinate system
-coordinate system, spatial domain, and precision Coordinate system is either geographic or projected; what we are measuring and in what units Spatial domain: essentially the values allowed in this system (max and min). Precision means how we are storing the values exactly.
Explain a Spatial Join or Joining Attributes by Location
A spatial join is a type of table join operation in which fields from one layer's attribute table are appended to another layer's attribute table based on the relative locations of the features in the two layers
Compare and contrast a definition query and an attribute query
An attribute query is a request for records of features in a table based on their attribute values. A definition query is when you select a subset of features for the layer display. This allows you to draw only some of the features in the dataset; defining what features you want to select in that layer
Explain all aspects of the dissolve operation.
An example of a spatial operation. We give the dissolve operation an attribute and a data set and we tell it to dissolve boundaries where the attribute has the same value on either side of that particular boundary. It outputs a new dataset without that boundary/arc
What is a "on the fly projection". Is this an accurate method to reproject geodatasets?
ArcMap can display data stored in one projection as if it were in another projection. The new projection is used for display and query purposes only. The actual data is not altered. The spatial alignment might be slightly off but not enough to notice at the scale of a world map; not accurate because it can misalign
Describe in detail constant, variable and multiple ring buffer zones
Buffer: a polygon geodataset; constant buffer zone: buffer spatial data by a constant amount; variable buffer zone: using an attribute from that feature to create the buffer zone; multiple ring buffer zone: can create a family of buffers of different distances
Describe the concept of a Domain in a geodatabase
Domains enforce data integrity by allowing only those values specified for the domain to be entered into the field. Domains are defined for the geodatabase and can be applied to multiple feature classes, tables, or subtypes. A domain in a geodatabase is a list or a range of valid values for an attribute. This prevents any new values from mistakenly being added to a table.
Describe the method of "Task, Target, and Tool" in creating new features
Find the task you're doing, describe the target (what will it produce), GIS tool that would be applicable to complete the task
Explain the basic concepts related to a geographic coordinate system (GCS) and projected coordinate system (PCS)
GCS is a reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid. A GCS definition includes a datum, prime meridian, and angular unit. A PCS is a reference system used to locate x,y and z positions of point, line, and area features in two or three dimensions. A PCS is defined by a GCS, a map projection, any parameters needed by the map projection, and a linear unit of measurement.
Describe the process of Geocoding
Geocoding is a procedure that lets you use addresses to identify location on a map - then it involves address matching, which is matching a record in a tabular file to a geographic feature using addresses as the link.
Briefly describe the required components of a new field
Name, Data Type (text or integer), and Properties (including domain)
Describe three advantages to the geodatabase format
One advantage is the ability to store multiple datasets. Another advantage is that the geodatabase is an ideal model for data sharing. A third advantage is that you can create an attribute domain. An attribute domain establishes/enforces ranges and values for an attribute field and minimizes mistakes in data entry.
Describe the common spatial analysis tools, buffers and overlays
Overlay operations include union, intersect, and identity. Overlays identifies an overlap between features in two layers and create a dataset in which the line of overlap defines a new feature. The buffers are constant, variable, and multiple ring. A buffer is an area drawn at a uniform distance around a feature - whether appoint, line, or polygon.
Understand selection by attribute operations and meanings of "<>", "like", etc
Selecting by attribute is a way to build a query expression. Query expressions consist of an attribute, a value, and a relationship between them; <> select ObjectID _________; like is searching for patterns between attributes
Describe what snapping is and what the snapping environment is for geodatasets
Snapping is a tool that allows you to create features that connect to each other, so your edits are more accurate, with fewer errors. Snapping is managed at the map level. This allows you to snap to features in a CAD drawing, coverage, feature class from another geodatabase, and so on. -snapping environment: the rules specifying which features, and which parts, snap to others; it makes it easier to snap back and forth
Describe the pros and cons of specifying a default value for a new attribute
Specifying a default value saves time when you are adding new features and want them all to be the same. Defaults can also be created without having a domain. However, if a domain is specified, the default value must be a valid domain value; -for each subtype, you can associate default field values and domains (pro), once defined the new subtype can become target of an ArcMap operation (con)
What are some Arc attributes that Geocoding requires that might not be associated with a vector street centerline geodataset?
Street name, beginning address to the right, ending address to the right, beginning address to the left, ending address to the left. Must have these associated with every arc in your reference to geocode. Street number, street name, street type, and suffix
Define and describe the POB (Point of Beginning) for a new polygon feature. Given a POB describe how COGO (coordinate geometry) measurements of angles and distances could be used to define new polygon features
The POB is the point of beginning of a new polygon, and the coordinates of which MUST be known on the earth. POB is the northings, eastings, or elevation (a known location on the earth's surface that we know to accuracy). Angle means an angle from true north. Distance + angle can define a new polygon feature/point.
Describe how basic calculations can be done with attributes using the Field Calculator
The field calculator works on string, number, and date fields and automatically calculates selected records if the layer or table has a selection set present.
What is a geocoding service? Briefly describe the steps required to build one
The service that we define given our input data and the street database that we have. It's the process where we define the details of the address file and address coverage (a lot of additional attributes). We have essentially written a computer program to take address files and coverage and do geocoding. It produces a new GIS layer of point type (output). It will also create a file of unmatched addresses. Steps: identify address file and its format, address coverage and its format 1. Build or obtain input and reference data: Obtain and make any needed modifications to the reference data to coincide with the address locator style requirements. Obtain the input address data. 2. Determine address locator style: Select an address locator style that accommodates the type of data you want to geocode and the attributes available in the reference data. 3. Build an address locator: Based on a specific address locator style, create an address locator and specify the geocoding options. 4. Locate addresses: Using your address locator, search for an individual address, place name, or locational-based information. The address locator can also be used to geocode a table of addresses. 5. Publish or maintain your address: locator The address locator can be shared as a locator package or published as a geocode service. If the reference data is updated, the related address locator can be rebuilt.
Describe in detail how attributes and vector information is handled during UNION, INTERSECT, and the IDENTITY operations. The IDENTITY operation was discussed in class.
These will give us different spatial outputs and the attribute tables will differ with the respect to the number of attribute table cells that have null values. Union: overlay polygons and keep all areas from both coverages Intersect: overlay points, lines, or polygons on polygons but keep only those portions of the input coverage features falling within the overlay coverage features. Identity: overlay points, lines, or polygons and keep all input coverage features.
Describe with respect to empty cells in the output table of an output coverage why you might use either the UNION, INTERSECT or IDENTITY operations
These will give us different spatial outputs and the attribute tables will differ with the respect to the number of attribute table cells that have null values; empty cells can mess up outputs
Explain why or why not a "dissolve barriers between" operation might be included in a UNION operation
We want to dissolve barriers to simplify a dataset/operation. On the other hand, you might not want to erase the arc because you can't put it back once you remove it.
When you load in a series of geodatasets that differ in map projection, how is the map projection of the Map Object in ArcGIS defined?
When the map projects/coordinate systems do not match, ArcMap uses a mathematical operation that recalculates geographic coordinates to projected coordinates (or vice versa). It then determines which equation is suitable for the projection; it changes layer 2's coordinates to match layer 1's
Building a location query, understanding the selection method and spatial relationship
You can use the "Select by Location" tool to create a location query. A location query selects features according to their spatial relationship to other features. Choose two layers and specify a spatial relationship (distance, containment, intersection, or adjacency). If you select the distance spatial relationship, you must specify a distance value and measurement units you want to apply. A location query might find which points are contained within a polygon or set of polygons, find features within a specified distance of a feature, or find features that are adjacent to each other.
Combining attribute and location queries
You can use the "Spatial Join" tool. It allows you to define a spatial relationship between two layers and combine their attributes in a new output layer. Once you join the tables, you can use the nonspatial attributes to symbolize, label, query, and analyze the features in a layer; joins attributes based on location
What type families of coordinate systems are pre-defined in ArcGIS, ArcMap, and ArcToolBox?
geographic, projected, and local
Definition of information that we used in our class:
reduction of uncertainty