CONFLATION OF A GAS UTILITY’S DATA: THE

CHALLENGE & REWARD

Clark Tenney, GIS Project Coordinator

John Ziakas, GIS Manager

Questar Gas Company – SLC, Utah

About Questar Gas

• Retail natural gas distribution company

• 968,500 customers • 28,735 miles of mains and

services

What is Conf lation?

Conflate (Merriam-Webster)a: to bring together : fuseb: confuse http://www.merriam-webster.com/dictionary/conflate

Conflation (ESRI)a: [data editing] A set of procedures that aligns the features of two geographic data layers and then transfers the attributes of one to the other http://support.esri.com/en/knowledgebase/GISDictionary/term/conflation

The goal of ConflationTo combine the best-quality elements of both datasets to create a composite dataset that is better than either of them. The consolidated dataset can then provide more information than can be gathered from any single dataset (Chen, Knoblock, 2008)

THE REAL STORY…

What would cause this to happen?

Why in the world wouldn’t you put the data in right, the first time?

1983 – VAX BASEDINTERGRAPH AM/FM SYSTEM

Early GIS Development

No entity in the state had incorporated a GIS

system

No available external digital data or aid to help Questar develop its GIS

County, state, and city control data (i.e. section corners, survey data) was

difficult to acquire

Early GIS Development

Large format plotters weren’t available yet, therefore, we

couldn’t distribute our maps

Large flatbed digital scanners had not been developed, so we didn’t have a way to scan existing maps

Early GIS Development

GPS had not yet been invented, so traditional survey methods

were all that could be used

Digital aerial imagery was yet to be developed

Aerial photography could be purchased but the software wouldn’t

support its use

Early GIS Development

So, how do you get your system’s mapping data into a new GIS system when none of it is electronic?

Manual Convers ion FromPaper to Electronic

Manual Convers ion FromPaper to Electronic

Prec i se (Prec i se+Accura te ) Accura te

The ChallengeOnce complete, Questar’s GIS data

became a ‘precise’ representation of

its gas system

As compared to the positional

accuracy of today’s GPS and imagery,

the data was considered to have less

accuracy and more precision

The Challenge

Survey data (i.e. section corners)

was either not available, or it was

only approximate in location

The Challenge

As the positional accuracy of

aerial photography greatly

increased, it could now be used

as a solid control for landbase

and gas facility data.

The Challenge

The length of time it took to redraw the

system = 10 years

Users made large unnoticed changes to

the GIS data

DIMP results didn’t always provide

accurate & confident results needed

when analyzing against outside data

sources

We b e g a n c o l l e c t i n g a s - b u i l t d a t a v i a h i g h a c c u r a c y G P S w h i c h d i d n ’ t l i n e u p w i t h o u r d a t a

The Business Decis ion to Conf late :

THE JUSTIFICATION

All these factors convinced Questar that it was time to initiate a conflation project which would spatially align all of our data to

aerial photography at a high enough accuracy as to correct inconsistencies and provide us with a higher level of confidence

in our GIS data & assure accurate DIMP program results

Conf lation Aftermath

The data will not be perfect post conflation

This assumption is a must when deciding to conflate your data Communicate this to others to temper their expectations

Follow-up adjustments & clean-up projects will be necessary

Have the resources and follow-up strategy well established

• Able to use GPS data to quickly and efficiently place GIS features

• Use aerial photography with confidence

• Better alignment with external data• Able to share data with external

entities• Improved substantiation of our

DIMP program results• More accurate modeling of our gas

network (gas network analysis)

The Rewards

QUESTIONS?