GIS Applications - Week 3

Address Matching - Accuracy Impacts

- ITS/EMS - emergency vehicles sent to wrong place - marketing - random errors insignificant, systematic errors are more serious (whole new neighbourhood omitted)

What is geocoding?

- a process of assigning spatial locations to data that are in tabular format but have fields that describe their locations - assigning a geographic location to a geographic feature on the basis of its address in order to display them on a map - is usually an intermediate step in geographic data processing

Address geocoding

- a process of plotting street addresses in a table as point features on a map - the goal is to automatically build a GIS database from a set of addresses - the ability to do this is based on the reference or base maps that are available for your local area

Address Matching - Accuracy Location Referencing

- communicating a location - reporting vehicle location with respect to a network - due to a database differences (e.g. scale), interoperability is a problem - a vehicle located on one road with respect to one map may appear in a different position relative to another map - coordinates are not sufficient - may also use - road names, cross street names, street address, linear reference offset (x distance from a reference point)

Geocoding - Postal Service Codes

- first 3 digits of the Canadian Postal Code define a Forward Sortation Area (FSA) - a useful unit for maping (average population around 20,000) and is hierarchically nested within provinces. starts down east, ends out west - the last 3 characters of the code help to guide your mail to a specific location (local delivery unit LDU) - in an urban area, the LDU refers to a block face, a large business, an office building, or another destination - for a rural destination, the LDU refers to the community to which the mail is to be delivered - value-added files - exist which allow the 6 digit code to be converted to census reporting zones and lat/long

Problems with Postal Codes

- great potential as discrete georeferences, however their purpose is internal to the postal system, codes frequently change, postal boundaries do no match Census boundaries, school districts etc. - still, there is great demand for statistics base on postal georeferences

Voice Geocoding

- increasingly popular - voice recognition, speech to text technologies - speak your - country, province/state, city, street, street number, intersection or cross street

Geocoding Engine - Abbreviations Standardized

- many elements of an address, such as direction or street type, are often written using an abbreviation and there is often a wide range of formats used to present them (dr, drv, drive) - attempting to geocode using such a wide range of abbreviations would greatly increase the search time - to avoid this, the address elements that are often abbreviated are assigned a standardized value - the address locator then assigns the standardized address components to match keys

Geocoding - Reference Data Sources

- so now we know that geocoding is performed using a reference layer - in Canada, the reference layers could be - a street network file, a postal code conversion file (PCCF), a forward sortation area file (FSA) or any other boundary file

Address Matching - Accuracy

- success rate usually 60% - 80%, non-standard spellings and representations, more efficient geocoding, spelling sensitivity, minimum match score, minimum score to be considered a candidate - typographical errors in one or other database - the precision of street addresses as georeferencing varies - is highest for apartments or houses in cities, is lowest for rural addresses or post office box numbers where address may indicate only that the place is somewhere in the area served by the post office - buildings may have different codes for different floors - overlapping and fragmented boundaries - new subdivisions, roads etc.

Geocoding Engine - Address Parsing

- the Address Locator compares the address entered with a rule base file which dissects the address into "address elements" - each style of address locator parses an address into a different set of address components - the address locator then sends the address elements to another rule base file to be standardized

US Streets (ESRI Style)

- two numeric ranges, one range for the left side of the street and one range for the right side of the street, represent addresses - street segments are stored as directed links with from and to nodes - address ranges are associated with the sides of the streets - linear interpolation is performed for each address on the basis of the proportion of the theoretical range of addresses along a street segment

Applications of Network Analysis

1. Pathfinding - shortest path 2. Location/Allocation modelling - one or more portions of a network to be served by a facility or business location 3. Tracing - all of portions of network connected with movement of particular feature 4. Spatial Interaction - flow of products, people, services, or information among places, in response to localized supply and demand 5. Distance Matrix modelling - distance matrix between pairs of locations

Procedure: Address Geocoding

1. match the street in both the event table and the reference layer 2. then compute the coordinates of the addresses by determining whether the street # is on the odd-or-even numbered side of the street 3. estimate the distance of the address for a street intersection by proportion with reference to the range of the street numbers in the relevant street segment 4. calculates the coordinates of address using coordinates of the street intersections

Some popular network software

ArcLogistics Route (ESRI) - relatively easy to use ArcGIS 10 - network analyst, utility network extension, ArcHydro CanMap RouteLogistics TruckStops (MicroAnalytics) RoadNet 5000 (UPS Logistics Company) VersaFreight (Versatile Systems) Visual Control Room (Intergis, MapInfo)

Geodemographics

Geodemographic classification is 'big business' in the marketing and service sector industries - business GIS, market geography - in public policy there has also been a resurgence of interest in neighbourhood initiatives and targeting - an increase number of professionals are realizing the potential of geographic analysis for their business or organization

Geocoding File Structure

it makes the process much easier if the columns/fields are separated into addresses in one column and postal codes in another - even better if the address number is a seperate field from street name

Parity

the property of evenness or oddness - in address matching, parity is used to locate a geocoded address on the correct side of the street (e.g. odd numbers on the left-hand side and even numbers on the right)

Geodemography

the study of spatial patterns in human populations - attribution of demographic characteristics to a group of individuals residing in the same geographic area - based on an overlay of demographic survey data against a geographically segmented list - the characteristics of human populations and population segments, especially when used to identify consumer markets - the study of the effects of location on marketing and retail

Demography

the study of the characteristics of human populations