W06 - Database Concepts and Data Sources

Question 1

how is spatial and attribute data used with GIS?

Answer 1

spatial data relate to the geometries of spatial features

attribute data describe the characteristics of the spatial features

Question 2

how does the georelational data model (eg. a coverage) store spatial and attribute data?

Answer 2

separately and links the two by the feature ID. the 2 datasets are synchronized so they can be queried, analyzed, and displayed in unison

Question 3

how does the object-based data model (eg. a geodatabase)

Answer 3

combines both geometries and attributes in a single system. each spatial feature has a unique object ID and an attribute to store its geometry

Question 4

how does the raster data model work?

Answer 4

cell value corresponds to the value of a continuous feature at the cell location

the value attribute table summarizes cell values and their frequencies in the raster.

Question 5

how is attribute data stored?

Answer 5

in tables, organized by rows (record) and columns (field).

Question 6

what are the 2 types of attribute tables in GIS?

Answer 6

feature attribute table and and tables of nonspatial data

Question 7

what is a feature attribute table?

Answer 7

an attribute table that has access to the geometries of features.

every vector data set must have a feature attribute table

in the georelational data model, the feature attribute table uses the feature ID to link to the feature’s geometry

in the object-based data model, the feature attribute table has a field that stores the feature’s geometry

have default fields that summarize the feature geometries (ex. length for line features and area & perimeter for polygon features)

Question 8

what are tables of non-spatial data?

Answer 8

these tables do not have direct access to the feature geometry but has a field linking the table to the feature attribute table.

ex. delimited text files, dBASE files, excel files, access files, other db files from SQL, oracle, etc.

Question 9

what is a database management system (DBMS)?

Answer 9

software package that lets us build and manipulate a database.

provides tools for data input, search, retrieval, manipulation and output

ArcGIS for Desktop uses Access for managing personal geodatabases

Question 10

how is the geodatabase implemented?

Answer 10

implemented in a relational database management system and stores both geometries and attributes in a single database

Question 11

what is a client-server distributed database system?

Answer 11

a client sends a request to the server, retrieves data from the server, and processes the data on the local computer

Question 12

what are methods of classifying attribute data?

Answer 12

by data type, by measurement scale

Question 13

what are the different data types?

Answer 13

determines how an attribute is stored, typically included in the metadata of geospatial data

ex. number, text (string), date, binary large object (BLOB)

Question 14

how can numbers (data type) be stored?

Answer 14

integers (no decimal digits), float/floating point

integers can be short or long.

float can be single precision or double precision

Question 15

what do BLOBs store?

Answer 15

store images, multimedia and feature geometrics as long sequences of binary numbers

Question 16

what are the ways to classify data by measurement scale?

Answer 16

nominal, ordinal, interval, and ratio data

Question 17

what is nominal data

Answer 17

different kinds / categories of data, such as land-use types or soil types

Question 18

what is ordinal data

Answer 18

differentiates data by a ranking relationship

Question 19

what is interval data

Answer 19

have known intervals between values (ex. 60F vs 70F differ by 10F)

Question 20

what is ratio data

Answer 20

same as interval data but ratio data are based on a meaningful zero value (ex. population densities)

Question 21

categorical data

Answer 21

includes nominal and ordinal scales

Question 22

numerical data

Answer 22

includes interval and ratio scales

Question 23

what are the types of database designs?

Answer 23

• flat file
• hierarchical
• network
• relational

Question 24

what is a flat file?

Answer 24

stores all data in a large table (ex. spreadsheet)

Question 25

what is a hierarchical database?

Answer 25

organizes its data at different levels and uses only one-to-many associations between levels (ex. zoning > parcel > owner)

Question 26

what is a network database?

Answer 26

builds connections across tables

Question 27

what is a common problem with hierarchical and network databases?

Answer 27

the linkages between tables must be known in advance and built into the database at design time. could make the database complicated and inflexible

Question 28

what is a relational database?

Answer 28

collection of tables (or relations) that can be connected to each other by keys

Question 29

what is a primary key?

Answer 29

represents one or more attributes whose values can uniquely identify a record in a table cannot be null and should never change

Question 30

what is a foreign key?

Answer 30

one or more attributes that refer to a primary key in another table

Question 31

common field

Answer 31

primary and foreign key with the same name

Question 32

what are the benefits of a relational database?

Answer 32

simple and flexible each table in the database can be prepared, maintained and edited separately from the other tables tables can remain separate until a query or analysis requires attribute data from different tables to be linked together (efficient for data management and data processing)

Question 33

what is the SSURGO and who produces it?

Answer 33

the Soil Survey Geographic database, produced by the Natural Resources Conservation Service (NRCS) SSURGO data collected from field mapping, archiving data in 7.5 minute quadrangle units, organized by soil survey area, which may consist of a county, multiple counties, or part of multiple counties database consists of spatial and tabular data for each soil survey area, spatial data contained a detailed soil map, made of soil map units (which may be made of one or more noncontiguous polygons). ` a soil map unit represents a set of geographic areas for which a common land-use management strategy is suitable.

Question 34

what is normalization?

Answer 34

process of decomposition, taking a table with all the attribute data and breaking it down into small tables while maintaining the links between them

Question 35

what are the objectives of normalization?

Answer 35

- avoid redundant data in tables that waste space and can cause data integrity problems - ensure attribute data in separate tables can be maintained and updated separately and linked when necessary - facilitate a distributed database

Question 36

normalization performance issues

Answer 36

higher normal forms than the third can slow down data access and create higher maintenance costs.

Question 37

what are the different types of relationships between records in tables?

Answer 37

one to one one to many many to one many to many origin and destination

Question 38

one to one

Answer 38

one record in a table is related to only one record in another table

Question 39

one to many

Answer 39

one record in a table may be related to many records in another table

Question 40

many to one relationship

Answer 40

many records in a table may be related to one record in another table (ex. several households may share the same street address)

Question 41

many to many

Answer 41

many records in a table may be related to many records in another table

Question 42

what is a join

Answer 42

brings together 2 tables by using a common field or a primary key + foreign key ex. joining attribute data from a nonspatial data table to a feature attribute table recommended for one to one or many to one relationships doesn't work for one to many or many to many because only the first matching record from the destination will be assigned to the origin record

Question 43

what is a relate?

Answer 43

operation that temporarily connects 2 tables but keeps the tables physically separate works for all types of relationships, but slows down data access

Question 44

what is a relationship class?

Answer 44

relationships between objects, predefined and stored in a geodatabase. for the object-based data model can be one to one, many to one, one to many and many to many for the first 3, records in the origin are directly linked to records in the destination for many to many, an intermediate table sorts out the associations between records

Question 45

field definition

Answer 45

# define each field in the table, usually include - field name - data width (# of spaces reserved for a field) - data type - number of decimal digits (part of the definition for the float type) field definition becomes a property of the field so it is important to consider how the field will be used before defining it

Question 46

methods of data entry

Answer 46

import attribute files, but if they don't already exist, then typing it in. for map unit symbols or feature IDs, best to enter them directly in a GIS. for nonspatial data, better to use word processing or spreadsheet packages (excel, notepad)

Question 47

what are the 2 steps to attribute data verification?

Answer 47

1) make sure that attribute data are properly linked to spatial data (feature ID should be unique and contain no null values) 2) verify the accuracy of attribute data

Question 48

what is an effective method for preventing data entry errors?

Answer 48

use attribute domains in the geodatabase attribute domains allows the user to define a valid range of values or a valid set of values for an attribute

Question 49

what does field management entail?

Answer 49

adding or deleting fields and creating new attributes through classification and computation of existing attribute data

Question 50

why is it good to delete unnecessary fields after downloading data from the internet?

Answer 50

reduces confusion in using the data set and also saves computer time for data processing

Question 51

creating new attribute data by classification

Answer 51

data classification reduces a data set to a small number of classes (ex. reclassifying elevations into groups) 1) define a new field for saving the classification result 2) select a data subset using a query 3) assign a value to the selected data subset

Question 52

creating new attribute data by computation

Answer 52

1) define a new field | 2) compute the new field values from the values of existing attributes

Question 53

what is the purpose of data exploration?

Answer 53

allows you to examine the general trends in the data, take a look at subsets, focus on possible relationships between data sets purpose is to better understand the data and provide a starting point for formulating research questions and hypotheses

Question 54

data visualization

Answer 54

discipline that uses a variety of exploratory techniques and graphics to understand and gain insight into data

Question 55

how does data exploration in GIS differ from data exploration in statistics?

Answer 55

1) data exploration in GIS involves both spatial and attribute data 2) includes map and map features besides descriptive statistics and graphics, data exploration in GIS must also cover map-based data manipulation, attribute data query, and spatial data query

Question 56

range

Answer 56

difference between the minimum and the maximum

Question 57

median

Answer 57

the midpoint value (50th percentile)

Question 58

first quartile

Answer 58

the 25th percentile

Question 59

third quartile

Answer 59

the 75th percentile

Question 60

mean

Answer 60

average of data values

Question 61

variance

Answer 61

measure of the spread of the data about the mean sum of (value - mean) ^2 divided by # of values

Question 62

standard deviation

Answer 62

square root of the variance

Question 63

z score

Answer 63

standardized score (x - mean) / standard deviation

Question 64

cumulative distribution graph

Answer 64

line graph that plots the ordered data values against the cumulative distribution values the cumulative distribution value is (i - 0.5)/n the values fall between 0 and 1

Question 65

bubble plots

Answer 65

a variation of scatterplots that uses varying-sized bubbles that represent a third variable

Question 66

boxplots

Answer 66

show min, first quartile, median, third quartile, max used to tell if the distribution is symmetric or skilled or if there are any outliers

Question 67

QQ plots

Answer 67

quantile-quantile plots compare the cumulative distribution of a data set with some theoretical distribution (ex. a normal distribution) points in a QQ plot fall in a straight line if the data set follows the theoretical distribution

Question 68

dynamic graphs

Answer 68

graphics displayed in multiple and dynamically linked windows where we can directly manipulate data points

Question 69

brushing

Answer 69

allows the user to graphically select a subset of points from one chart and view related data points in other graphics

Question 70

geovisualization

Answer 70

data visualization that focuses on geospatial data and the integration of cartography, GIS, image analysis, and exploratory data analysis

Question 71

what are the different types of map-based data manipulations?

Answer 71

data classification, spatial aggregation, and map comparison

Question 72

what are the different methods of doing map comparisons?

Answer 72

1) superimpose layers on top of one another and have them be represented on the map differently, or turn the layers on and off, or use transparency 2) use map symbols that can show two data sets ex. bivariate choropleth map ex. cartogram, where the unit areas are sized proportional to a variable (ex state population) and the area symbols are used to represent the second variable 3) temporal animation can be used if there is time-dependent data

Question 73

attribute data query

Answer 73

process of retrieving data by working with attributes (ex. SQL commands)

Question 74

SQL

Answer 74

data query language designed for manipulating relational databases, used in the GIS to communicate with a database select from where ex. select Parcel.Sale_date from Parcel where Parcel.PIN = 'P101' ex. select Parcel.Sale_date from Parcel, Owner where Parcel.PIN = Owner.PIN AND Owner_name = 'Costello' query joins the two tables and then actually queries it

Question 75

procedural differences when querying a local database in a GIS package

Answer 75

1) only have to enter WHERE in the query expression box because typically the field and table have already been selected 2) an attribute query dialog is typically designed for a single table, so if the query involves attributes from two tables, they have to be joined first.

Question 76

query expressions

Answer 76

the where conditions with Boolean expressions and connectors

Question 77

Boolean expression

Answer 77

contains 2 operands and a logical operator operands can be a field, number, or text logical operators can be =, >, =, <> (not equal to) can also contain arithmetic operators

Question 78

boolean connectors

Answer 78

AND, OR, XOR, NOT XOR is the opposite of AND. only records that satisfy one and only one of the expressions are selected

Question 79

what are the types of operations that can act on a data set?

Answer 79

add more records to a subset remove records from a subset select a smaller subset

Question 80

relational database query

Answer 80

works with a relational database, selects a data subset in the table and also selects records related to the subset in other tables

Question 81

what is the difference between join operation and relate operation?

Answer 81

join operations combines the attribute data from 2 or more tables into a single table. relate dynamically links the tables but keeps the tables separate

Question 82

spatial data query

Answer 82

process of retrieving a data subset from a layer by working directly with feature geometries. the results can be simultaneously inspected in the map, linked to the records in the table and displayed in charts can select features spatially using a cursor, a graphic or the spatial relationship between features

Question 83

feature selection by graphic

Answer 83

draw a shape (graphic) to select objects of interest (ex. restaurants within a 1 mile radius of a hotel)

Question 84

feature selection by spatial relationship

Answer 84

selects features based on their spatial or topological relationships to other features ex. roadside rest areas within 50 mile radius of selected rest area; rest areas within each county spatial relationships used for querying include containment, intersect, and proximity

Question 85

containment (spatial query)

Answer 85

selects features that fall completely within features for selection

Question 86

intersect (spatial query)

Answer 86

selects features that intersect features for selection

Question 87

proximity (spatial query)

Answer 87

selects features that are within a specified distance of features for selection

Question 88

spatial adjacency

Answer 88

features to be selected and features for selection share common boundaries and the specified distance is 0

Question 89

raster data query - query by cell value

Answer 89

use the raster instead of a field in the operand to query a feature can query multiple rasters, which may be integer, floating point, or a mix of both. querying multiple rasters directly is unique to raster data

Question 90

raster data query - query by select features

Answer 90

features can be used to query a raster and it returns an output raster with values for cells that correspond to the query and no data in the other cells