GEOL 452/552 - GIS for Geoscientists I. Lecture 9

Transcription

1 GEOL 452/552 - GIS for Geoscientists I Lecture 9 1

2 Review (voting) Joining tables (database joins) Tutorial ch 4: (43-50) HW 5: ch 4, ex 1,2 (make new float field!), 4, 5, 8 & 10 Text 2

3 Find the WRONG statement: a single number The result of a (database) SQL query on a standalone table is: a selection of records Some light blue stuff a selection of features 3

4 Statistics operation vs. Summary operation - which statement is wrong? Summary uses one field to group and shows group member statistics Statistics shows global statistics for a single field Summary creates a new standalone table Statistics creates a COUNT_ field 4

5 You create a table column - what type for: Population of countries in the world? use Long - large number but you don t need decimals. Average price for 1 gallon of gas? use Float - need 2 decimal places, number itself is not very large. Integer? (Short or Long) Number of counties in a state? use Short, - only a small integer Highway names? use text - contains letters (how long?) Text? (String) Floating point number? (Float or Double) Distances between cities, in meters use Double - if high precision for these large numbers needed or Long - if fractions of meters don t matter. 5

6 USA county data (per county: NAME, POP and STATE) - use query, statistics or summarize for: Find all counties with > 20,000 people? SQL query ( POP > 20000) Find total number of people in each state? summarize : Group field? Stats field? Type of stat? Group field: STATE ; stats field: POP ; type of stat: SUM Summarize? Statistics? What would COUNT_ contain here? Total number of people in US? statistics for POP SQL query? 6

7 Destination Joining tables Source Destination table Source table Input Join tables on common field (STATE_FIPS = key field) Input Output Joined table 7

8 Join (Initially) temporary relationships between 2 tables to create a single table Think join Source to Destination (as in attach (connect) a car to a train engine, follow the arrow) To Join tables must share a common field (key field) 8

9 Joins: easy way to make spatial data from a standalone table... if you have a field Joins are temporary (ad hoc) and can be removed again To make permanent: export shapefile with joined tables 9

10 What is the key field here? Res-ID Name SSN Restaurant Res-ID Parcel_no Jake s Pizza Momma s Pie Hut Big Burger Barn Jake Smith Nancy Gold Dan Smurt Karen White Judy Lewis Joshua Jones Parcel_no Address Value Owner Maple Ave 67,000 Roger Clark Main St 114,510 Roger Clark Sherry Ave 59,000 Judy Lewis Note: keys do not have to have the same name, just the mean the same concept 10

11 Rule of Joining Each record in the destination table must match (go back to ) one and only one record in the source table. Destination Source One to one Destination table Source table Many (arrow heads) to one (tail) 11

12 How to join or relate tables R-Click Destination layer Key field in destination layer: Source table/layer: Key field in source layer: 12

13 Joining class exercise Copy data\follow along\ch4b_join_ex folder in your student folder. Open Ch4_join_relate.mxd file in ArcMap Open attribute tables for both layers side by side Use State (STATE_NAME) name as key for joining 13

14 Connecting many source records to one destination record Destination table Source table? Record to join to destination is ambiguous Violates the Rule of Joining: ( arrow head collisions ) Must use a relate instead Useful when selecting across tables (see later) 14

15 When can we Join vs. Relate? Depends on the cardinality of the pair! Four possible types of cardinalities: 1-to-1, Many-to-1, Language: We say: 1-to-Many, Many-to-Many This is a Destination-to-Source cardinality, in a Many-to-1cardinality, 1 source goes to many destinations! 15

16 CARDINALITY: Types of Relationships (follow arrows back from tip!) One-to-One Relationship Destination Table Source Table Destination Table One-to-Many Relationship Source Table One Many Many-to-One Relationship Destination Table Source Table Many-to-Many Relationship Destination Table Source Table Many One An engine gets only 1 car: can use Join operation (no arrow head collisions) An engine gets 2+ cars: can only use Relate operation (arrow head collisions) 16

17 Source/Destination? Key? Cardinality? Join? Restaurant Res-ID Parcel_no Jake s Pizza Momma s Pie Hut Big Burger Barn Parcel_no Address Value Owner Maple Ave 67,000 Roger Clark Main St 114,510 Roger Clark Sherry Ave 59,000 Judy Lewis Res-ID Name SSN 20 Jake Smith Nancy Gold Dan Smurt Roger Clark Judy Lewis Joshua Jones Restaurant Res-ID Parcel_no Jake s Pizza Momma s Pie Hut Big Burger Barn Res-ID Name SSN Restaurant Res-ID Parcel_no Jake s Pizza Momma s Pie Hut Big Burger Barn Jake Smith Nancy Gold Dan Smurt Roger Clark Judy Lewis Joshua Jones

18 Cardinalities? (Draw arrows) Students to college classes? many-to-many. States to governors? one-to-one. Departments to professors? one-to-many. Counties to states? many-to-one. Chris Tom Anne Mary Arnold Jesse Geology Math Story Polk Geol552 Psych101 California Minnesota Chris Ken Jane Mary Iowa 18

19 Smart Selection using Relate STATE_ABBR related to STATE_ABBR in 2. table Select record Automatically selects all records in 2. table with MN Second Table: 19

20 Joining class exercise (cont.) What s the Cardinality of Counties to State? State to Counties? Which case can we use for a join? Let s try it... After joining, how many records in the joined table? What happens when we join the other way? (Join the other way - how many records now? Problem? Instead: Use a relate to select across tables 20

21 Wrap-up Did Miniproj 1 (HW4) finally work? Tutorial ch 4: (43-50) HW 5: ch 4, ex 1,2 (make new float field!), 4, 5, 8 & 10 HW 5 due Oct. 1 21