geocoding and dynamic segmentation

GEOCODING AND DYNAMIC SEGMENTATION

BYB ANEESHA SATYA131854

CONTENTS

•GEOCODING•APPLICATIONS OF GEOCODING•DYNAMIC SEGMENTATION•APPLICATIONS OF DYNAMIC SEGMENTATION

BASIC GIS FEATURE TYPES 

•  Point  -  Cities, control points (BM), weather stations  - 

Location, distance (buffer), point pattern, interpolation  •  Polygon 

-  States, land use (zoning), land cover, eco region  -  Location (area coverage), distance, shape metrics, 

overlay  •  Line 

-  Roads, streams, utility lines, path  - 

Location (linear referencing), distance, shape metrics  (e.g., sinuosity), connectivity

LINEAR FEATURE ANALYSIS  :

•  Linear referencing - location  - Geocoding (e.g., address matching)  - Dynamic segmentation 

Geocoding - the process of assigning spatial locations to data that are in table format but have fields that describe their locations. Dynamic segmentation – the process of computing the location of events along a route, can locate spatial features (linearly referenced events) from a data source that lacks x-, and y-coordinates.

•  Address matching  •  Corner (intersection) matching  •  ZIP Code geocoding •  Reverse geocoding 

TYPES OF GEOCODING

ADDRESS GEOCODING: plots street address as point features in a map.Most common type is address geocoding (address matching) : Internet mapping such as MapQuest, Google, Yahoo, MS’sMapPoint…Requires two sets of data such as street name, zip codes segmented data -Individual street addresses in a table(one record per address) -Reference databaseAddress geocoding interpolates the location of a street address by comparing it with data on the reference database

A sample address table records name, address, and ZIPcode.

GEOCODING REFERENCE DATABASE: consists of street map and attributes for each street segment such as street name , address ranges, zip codes

1.TIGER/Line files (U.S. Census Bureau) -Contain legal and statistical boundaries, streets, roads, streams, water bodies - Has Built- in topology -Also contains attributes for each street 2. Segment street name, beginning and ending address numbers on each side, ZIP codes on each side 3. Also available from commercial companies like Tele ATLAS

The TIGER/Line files include the attributes of FEDIRP, FENAME, FETYPE, FRADDL, TOADDL, FRADDR, TOADDR, ZIPL, and ZIPR, which are important for geocoding.

GEOCODING PROCESS:-GIS software packages have built-in geocoding engines for address matching(ARCgis ,Mapinfo)-Two steps•Pre processing-breaks address into segmentsEX:620 N• Software first locates street segment in reference database that contains the address.- Then it interpolates where the address falls within the address range and gives a point location.

Linear interpolation for address geocoding.

ERRORS IN ADDRESS RECORDING

- Misspelling of street name- Incorrect address number- Incorrect direction prefix or suffix- Incorrect street type- PO Box type instead of street address- Incorrect ZIP code

ERRORS IN REFERENCE DATABASE

-Outdated because it lacks information on new streets-Street name changes- Street closings-ZIP code changes or incorrect ZIP codes- Missing address ranges- Gaps in address ranges

ADDRESS MATCHING OPTIONS- Geocoding engine has provisions for relaxing the

matching conditions but uses a scoring system.- User may decide the rigor or accuracy of address

matching- Spelling sensitivity- Acceptable hit rate- Geocoding process converts addresses to points- End offset and side offset options

•The end offset moves a geocoded point away from the end point of a street segment•The side offset places a geocoded point away from the side of a street segment.

-point in polygon analysis(linking point address to census)

OTHER TYPES OF GEOCODING-Intersection matching also called corner matching, matches address data with street intersections

here end points of two different addresses in intersection are matched-ZIP code geocoding matches a ZIP code to its centroid location

instead of using street network x,y coordinates are used-REVERSE geocoding converts location into descriptive address

An example of Intersection matching.

GEOCODING APPLICATIONS  •  Location based services (GPS, e911)  •  Geodemographic analysis  •  Public health  •  Crime analysis

• Data preparation for spatial analysis• Real estate• Health services• Travel times and distances (emergency

response)• Crime mapping and analysis00

  •  DS is the process of computing the location 

of events along a route. Should have a built-in measurement system

•Routes((multipart)polylines)-linear feature with linear measurement system stored with its geometry.

Ex:Mileposts along highways, mileage measurements along stream

• Sections (polylines) •Events-linearly referenced data that occur along routes Ex: Events include speed limit changes, traffic accidents, fishery habitat conditions along streams

• Dynamic segmentation links events to the routes

DYNAMIC SEGMENTATION

ROUTES- Must have built-in measurement system-distinction in measurement system storage between ESRI’s coverage model and geodatabase model-Coverage model treats route as sub-class in a line coverage- Geodatabase data model treats route as polyline feature

An example of a route subclass using the coverage modelFig a- arcs showing the linear features.Fig b-route super imposed with linear features.Fig c- tabulates the linear measure of three sections.

An example of a geodatabase routefeature class.

• Geodatabaase model treats a route polyline feature class.•Simply stores linear measures in the geometric model• x,y values locate the linear feature in the coordinate system ,m value relates to route’s linear measurement

Creating Routes-Interactively or through data conversion-Interactive method: first digitize route or select existing lines, then apply measuring command to the route to compute route measurements.- Data conversion method: can create routes at once from all linear features or from features selected from data query.

The interactivemethod requires theselection ordigitizing of the linesegments that makeup a route (shown ina thicker linesymbol).

Interstate highwayroutes in Idaho

ROUTE TYPES- Simple route :one direction, no loop or branch-Combined route : joined with another route, has different conditions depending on direction.- Split route : subdivided into two routes- Looping route : intersects itself

An example of a split route.

Events-Linearly referenced data usually stored in a table- Dynamic segmentation process is independent of x-, y-coordinate system- Events may be point or line events

Point Events-Accidents, stop signs- Occur at point locations- To relate point event to a route, point event table must have route ID, location measures of events, and attributes describing the events

Line Events- Pavement conditions-Cover part of a route-To relate line events to a route, line event table

must have route ID, and from and to measures.

CREATING EVENT TABLES -Two common methods - Create event table from existing table n Method assumes that event data are

present in tabular form and linear measures are available - Create table by locating point or polygon features along the route- Similar to vector-based overlay operation - Input layers are a route layer and a point or polygon layer- Instead of creating an overlay layer, a table is created

An example of convertingpoint features to pointevents.

An example of creating alinear event table byoverlaying a route layer and apolygon layer

APPLICATIONS OF DYNAMIC SEGMENTATION-Dynamic Segmentation can store attributes along with routes which can then be displayed, queried, and analyzed-Useful for data management, data display, data query, and data analysis

Data Management-Useful in two ways- Different routes can be built along the same linear feature- Different events can reference the same route, or, more precisely, the same linear measurement system stored with the route- Fisheries biologists can store various environmental data with a stream network for habitat studies.

Data Display

- Once table is linked to route, table is georeferenced and can be used as a feature layer.- Similar to geocoding an address table

The thicker, solid line symbol represents those portions of the Washington State’s highway network that have the legal speed limit of 70 miles per hour.

Data Query-Can perform attribute data query and spatial data query on an event table and its associated event layer- Recent traffic accidents follow pattern

Data query at a point, shown here by the small circle, shows the route-ID, the x- and y-coordinates, and the measure (m) value atthe point location. Additionally, the beginning and ending measurevalues of the route are also listed.

Data Analysis-Routes, events may be inputs for analysis-Efficiency of public transit routes- Buffer the route, overlay with census blocks and demographic data for planning and operation of the public transit system- Data analysis between two event layers- Relationship between traffic accidents and speed limits (similar to vector-based overlay operation)