Transcript Databases
DATA • Spatial Data – where things are • Non Spatial Data or Attribute Data – What things are • Data in a computer database are managed and accessed through a DataBase Management System (DBMS) • The DBMS allows users to deal with data without needing to know how the data are stored and structured in the computer. Database Concepts • GIS creates a model of the world • GIS uses raster and vector representations (spatial data) to model location of geographic features • All geographic features are linked to non spatial data or attributes that describe or are related to the spatial data/features. Database Creation • Data investigation – What do you need to know? • Data modeling – conceptual model by examining the relationships between features (entities) and the the characteristics of the features/entities (i.e. attributes) • Database design – field names, types and structure along with the DBMS • Database implementation – populating the fields, fine tuning, updating, etc. Advantages of computer-based databases • Different data access methods are possible. • Data are stored independently of the application for which they will be used. • Redundancy will be minimized. • Access to data can be controlled (passwords) • Database is relatively easy to maintain and updating is possible • Standardized query languages can be used. GIS Links features to their attributes Managing Non-spatial data Flat Files or Spread Sheets •Each geographic feature is matched to one row “record” of data. •All records in this database have the same number of “fields” (columns in GIS databases are called fields, rows are called records) •When the number of fields becomes lengthy a flat file is cumbersome to search. Managing Non-spatial data Hierarchical files Hierarchical files Hierarchical files store data in more than one type of record, “one to many” relationship. One field is key to all records, but data in one record does not have to be repeated in another. Managing Non-spatial data Relational Files • Connects different files or tables without using internal pointers or keys. Instead a common link of data is used. A “matrices of tables” is used to store the information. Stock Inventory Reorder item Targeted marketing by zip code GIS Database Scan bar code Purchase Lamp at Pier 1 Imports Scan credit card Debit authorized Profile on your buying habits We are an information producing society and information is worth lots of $$$ Structured (Standard) Query Language • Database queries through the SQL of DBMS – – – – Sorting renumbering Searching Subsetting • This allows for the creation of new data • Geographic search is the key of GIS • Which customers from the 93940 zip code spent over $100 in 2001? Tabular data compatible with ArcView • dBASE (.dbf) use dBASE IV but III works too. • Delimited text • INFO format (ARC/INFO) • ArcView can also link to DBMS like Ascess, Visual FoxPro, Excel, dBASE ArcView Table data types • • • • Short and Long Integer (13252637) Text (afdje83kfur74) Date (based upon standard time format) Object ID, Float, Double, Blob How projects and files are stored in ArcView File extentions • • • • • • • Project.mxd is an ArcView Project file Filename.shp Filename.shx Filename.dbf .ain and aih (table has been linked) .sbn and .sbx (table has been joined) (.avi a script has been added – ArcView 3.2) Joining Tables • To join a table you need a common attribute field. • A table join is preserved only within a map document, the table on disk are not changed. To permantly append – export as a data set. • One to one or many to one relationships • See page 224 in GTKArcGIS Relating Tables • One to many relationship • One record in the attribute layer table relates to many in the Non-spatial table.