GIS exam 2 DX
What is the difference between professional and recreational GPS receivers?
Professional GPS receivers have higher quality clocks which are atomic. This is more accurate because the gps unit determines the distance by using the time stamp and comparing times to calculate distance (distance/ time) = velocity (speed of light). A less accurate rec GPS will have less accurate time.
Which type of snapping (end, vertex, or edge) would work best in the following situations? (a) digitizing streams, (b) digitizing parcels, (c) digitizing streets, (d) digitizing traffic lights at intersections, (e) digitizing stream gages on streams
(a) end snapping (match new vertex to end of existing line) (b) vertex snapping (c) edge snapping (d) vertex snapping (e) edge snapping
What are the cardinalities fo the following (are they joins or relates)? *1* Number of earthquakes (join)to total damage in each state(target) *2* State info (join) to counties (target) *3* states (target) and counties(join) *4* Classes to Students
*1* This is a one to one cardinality. There is one amount of damage per each earthquake. *use a join* *2* this is a many to one cardinality. There are many counties (target) to one state (join) *use a join* *3* This is a one to many cardinality as there are many counties (join) for each counties. *use a relate* *4* This is a many to many cardinality. There are many classes each student has and many students in each class *use multiple relates to show this*
What causes errors in GPS?
*1* satellite signal slows as it enters the atmosphere *2* minor variations in the location of satellites *3* inaccuracies in the timing clocks *4* signal multipath (slight timing errors resulting when the GPS signal is reflected off objects such as tall buildings, or other large solid bodies before it reaches the receiver) *5* satellite geometry (Relative position of satellites at any one time, tight clustering - poor geometry
Distinguish between an attribute query and a spatial query.
*Attribute query* query uses values in the attribute table to test a condition, such as finding cities with population greater than 1 million. *spatial query* uses information about how features from two different layers are located with respect to one another.
What is the difference between an attribute table and a standalone table?
*Attribute tables* contain information about features in a geographic data set. They are linked to a shapefile*they always contain only one row of info per spatial feature* *Standalone tables* simply contain info about 1 or more objects in tabular format, they exist independently of geographic data set *do not have a shape field like point, line, polygon(cannot be mapped)
What are the main types of topological errors?
*Dangles*- lines that fail to connect properly, Overlap and Gap Occur when two polygons don't align correctly
List the six different types of queries discussed in this chapter, and briefly describe each in your own words.
*interactive query* the user selects objects form a table or map using the mouse *attribute query* the user tests to see if values in a table meet set criteria and selects those that do *spatial query* the user selects objects based on their physical relationship to other objects. *definition query* used to create layers or standalones for your map *Buffer* this is a spatial query that marks an area for a certain distance around an object
Relational operators
=, >=, <=, >,<
Describe the difference between a 'join' and a 'relate'. When is a 'relate' the only option?
A *join* combines tables using a common field called a key field, which must be the same for both tables. They are temporary and direction dependent. A *relate* does not create a new table. The 2 tables are still associated by a common field, but are separate. If one or more records are selected in 1 table, then the associated records are selected in the other table. *relates must be used for many to many and one to many cardinalities*
What options may be used to handle a one-to-many cardinality in a spatial join?
A *one-to-one join* operation specifies that each join feature will be copied once to the target feature class. If the target feature matches more than one record in the join layer, then a merge rule will be applied to produce a single record to append, for example, by averaging or summing the numeric values of all the matches to produce a single value. You can also use a *one to many join*(, which will produce multiple copies of the target feature until there are enough to match the join feature *USE CAUTIOUSLY* this creates many duplicate copies of the target feature which may result in a very large dataset
What is the function of a case field? Make up an example table with seven records and use it to illustrate your explanation.
A case field allows you to group records and calculate statistics for separate groups in a table by separating them. Usually the case field has categorical data like state name to allow you to look at data per state. *Example* you could have a table summarizing earthquake damage and then group the earthquake damage by state (this would sum the damage and death and count)
If a point feature type is joined to a polygon layer, with the points as the target layer, what will the feature type of the output layer be?
A spatial join copies features from the target feature class and appends attributes from the join feature class. This means that the output layer will be a point feature type.
What is meant by GNSS? Provide examples of GNSS.
Global Navigation Satellite System, an example of this is GPS which is the American system (GLONAS and Galileo)
why are joins and relates necessary?
In order to analyze the relationship between data. To be able to correlate data.
Which one(s) of the following tools or functions create a new data set in a geodatabase? Select Layer By Location, Make Feature Layer, Buffer, Clip, Definition Query, Export
Make Feature Layer, Clip, *export* (definitely export, unsure of the others)
If you are editing a dataset that is in UTM Zone 16 N projection but the Data Frame is set to North America Equidistant Conic Coordinate System, in what units will the edits you make be stored in?
North American Equidistant Conic Coordinate, because it will converted as it is saved to shapefile
What is a definition query and what is its purpose?
Queries are used to extract a set of features from a map or objects from a table, based on criteria set by the user.
What are the three components of GPS?
Satellites orbiting the earth, control and monitoring stations on earth, and GPS receivers owned by users
What is a target table?
Table that receives the appended information (destination)
In what ways does the Clip tool differ from the Select Layer By Location tool?
The *clip tool* works like a cookie cutter to truncate the features of one file based on the outline of another. This is different from select layer by location because this tool makes you select of not select the entire feature
Which are the three panels of the Context pane that will be the most helpful when editing?
The General editing menu which has selection, repositioning, and modification tools. The sketch menu gives you exact angles, distances, and lengths. The Vertex menu lets you add, delete, and move vertices
What is the AutoComplete tool designed to do?
The autocomplete polygon tool digitizes only the new part of an adjacent polygon (so you draw the new polygon into the old one and they will share an edge)
What are Boolean operators? Provides five examples and understand how they are used in linking multiple criteria.
The boolean operators are AND, OR, XOR, and NOT
What is the primary goal of using topology to edit polygons?
The goal is to create and maintain topological integrity between features so that their relationship in the database matches their relationship in the real world.
Joining points to polygons may be performed using either the 'intersect' or 'containment' operator, with very similar results. In what situation will the results be different, and how will they differ?
The results would be different if the point falls on the line of the polygon. The containment operator would not count the point, while the intersect operator would count the point in two polygons.
What is topology?
The spatial relationships between features in terms of adjacency, connectivity, intersection, or overlap
What is the rule of joining?
There must be only one record in the join table (or source table) for every record in the target or destination table *otherwise you lose data because only one of the records will be used*
In what language are queries in GIS composed in?
They are written in SQL or structured query language (expressions used to make selections)
What is selective availability? What was the impact of SA?
This purposely made the GPS position less accurate (100 meter accuracy) this was put in place by the military to hide their bases and operations. This caused GPS users to have to use formulas to calculate their accurate GPS
What is the purpose of the intersect function?
This tests if one feature touches another
How does one prevent gaps or overlaps when digitizing new polygons?
Use snapping and either vertex or edge snapping so that the x-y coordinates match up (or the autocomplete tool)
What coordinate system is GPS data originally gathered in?
WGS 1984 spheroid and datum
What are some of the ways the accuracy of GPS has been improved?
We have more satellites to get more precise readings (the united states has 31 satellites), the atomic clock in gps units are more accurate, and the selective availability has been removed.
You have a table of cities and a table of counties, both with a state abbreviation field. Can you join them if cities is the target table? If counties is the target table? Explain your answer
Yes, you can use state abbreviation as they key to so a join if cities is the target table, because there should only be one county for every city, but there may be many cities in each county. This would be a *many to one join*. However, if counties is your target table and cities is your join table then you would have multiple records in the joint table for every record in the target table. This would be a *one to many join*, and would violate the rule of joining. This would mean a loss of data.
How do you prevent vertices of features close together from being snapped?
You can change the snapping tolerance. This tool ensures that lines and vertices match You can either reduce the snapping tolerance so that the vertices would have to be closer to snap. Or you could turn the snapping tool off entirely.
How does one initiate editing in ArcGIS Pro?
You can use the editing ribbon to initiate editing. Here you can find the snap, create, and modify tools
What is cardinality?
cardinality is the numeric relationship between two tables, its direction matters!
How does one create separated polygons (remember the 'doughnut' we created in class?) as a single feature?
click the polygon feature template in the Create Features window, then click the construction tool and method and digitize the outside of the polygon without finishing the sketch. Right click and select finish part. Click inside the polygon and sketch the inner boundary, then finish the sketch.
Distinguish between a simple and a compound query.
compound queries contain multiple clauses connected by the logical operator AND or OR. Simple queries contain only one clause
Buffer
is a type of spatial query used to delineate areas that fall within a certain distance of a set of features.
What primary characteristics distinguish a spatial join from selecting by location?
is similar to an attribute join, except that, instead of using a common field to decide which rows in the table match, a spatial relationship between the features is used. *It is different from selecting by location (and attribute join) because it creates a new feature class*
What is an operator? Describe and give examples of each of the following: arithmetic operators, logical operators, spatial operators, and Boolean operators.
operators are used to create expressions to evaluate relationships. *Arithmetic operators* allow for manipulation of information using plus, minus, * and division. This could be used to sum occurrences. *logical operators* include >,<, and = and test the relationship between attributes. For instance, the objects that have the same state name. *spatial operators* test the physical relationships between objects using containments, proximity, and intersection. *Boolean operators* evaluate pairs of true/false conditions they include AND, OR, XOR, and NOT. (compound queries)
containment
operators test whether one feature includes another.
Intersection
returns any feature in A that touches, crosses, or overlaps any part of a feature in B.
What is a join table?
table containing the information to be appended (source)
Proximity
tests how close features in A are to features in B.
What makes one type of receiver more accurate than another?
the clock (atomic or not)
Explain the purpose of a map topology.
this automatically tracks features that are adjacent or connected to each other. It lets you simultaneously modify connected lines and when nodes are moved the lines move together.
Erase
works in the opposite sense of a clip, keeping features that fall outside the erase layer and eliminating those inside.
Clip
works like a cookie cutter to truncate the features of one file based on the outline of another..