CONFLATION OF A GAS UTILITY S DATA: THE CHALLENGE & REWARD

Transcription

1 CONFLATION OF A GAS UTILITY S DATA: THE CHALLENGE & REWARD Clark Tenney, GIS Project Coordinator John Ziakas, GIS Manager Questar Gas Company SLC, Utah

2 About Questar Gas Retail natural gas distribution company 968,500 customers 28,735 miles of mains and services

3 What is Conflation? Conflate (Merriam-Webster) a: to bring together : fuse b: confuse 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 The goal of Conflation To 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)

4 What would cause this to happen? Why in the world wouldn t you put the data in right, the first time? THE REAL STORY

5 1983 VAX BASED INTERGRAPH AM/FM SYSTEM

6 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

7 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

8 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

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

10 Manual Conversion From Paper to Electronic

11 Manual Conversion From Paper to Electronic

12 Precise (Precise+Accurate) Accurate

13 The Challenge Once 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

14 The Challenge Survey data (i.e. section corners) was either not available, or it was only approximate in location

15 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.

16 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

17 We began collecting as- built data via high accuracy GPS which didn t line up with our data

18 The Business Decision to Conflate: 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

19 Conflation 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

20 The Rewards 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)

21 QUESTIONS?