1. Exactly defining Precision with all Accuracy
As viewed by a cadastral mapper
Presented by:
Emilio J. Solano
Chief Cadastral Engineer
Mapping & G I S Services

2. Exactly defining Precision with all Accuracy
Main Topics
Common Definitions
Differences
Application of concept
Who do we work for?
Questions

3. Common Definitions Precision:
(1)The closeness of a repeated set of observations of the same quantity to one another.
(2)The number of
Significant digits
used to store numbers.
(1): The assessment of the quality of a surveyor’s work is based in part on the precision of their measured values.
(2): Is important for accurate feature representation, analysis, and mapping.

4. Common Definitions SINGLE PRECISION STORAGE: DOUBLE PRECISION STORAGE:
2.147 x 109 = 5m in a 1,000,000m extent
DOUBLE PRECISION STORAGE:
*9.007 x 1015 = >> 1m in a global extent
more or less 0.25m in a 12,760,000m extent
Accuracy is a measure of correctness, while precision measures exactness.

5. Common Definitions
Accuracy: The degree to which a measured value conforms to true or accepted
values.
Accuracy is a measure of correctness, while precision measures exactness.

6. Common Definitions HIGH ACCURACY HIGH PRECISION HIGH ACCURACY
Accuracy is a measure of correctness, while precision measures exactness.
HIGH ACCURACY
HIGH PRECISION
HIGH ACCURACY
LOW PRECISION

7. Common Definitions LOW ACCURACY HIGH PRECISION LOW ACCURACY
Accuracy is a measure of correctness, while precision measures exactness.
LOW ACCURACY
HIGH PRECISION
LOW ACCURACY
LOW PRECISION

8. Common Definitions Exact: Capable of accuracy of detail;
very accurate; methodical; correct.
Exactitude: The quality of
being exact; precise;
accurate.
From Latin exigere:
To measure, to determine
The concept of exact or exactitude comes to play when applied to the WAY or METHOD followed to generating maps.

9. Common Definitions
Ambiguity: When an object may appropriately be assigned two or more values for a given attribute.
Intention:
Determination to do a specified thing or act in a planned manner.
Anything intended or planned; purpose.
An instrument, such as a concept, for knowing and referring to a thing as it exists in the mind.
Ambiguity may be caused by changeable conditions in reality, like coastal areas experiencing tidal fluctuations may be dry land at some times and under water at other times.
Intention is for example, when a deed describes a boundary between two known points, but the length given disagrees with an existent length. It may also be caused by disputes, as when two parties claim ownership of portion of the same tract of land.

10. Differences Precision: It is a measure of exactness
Accuracy: It is a measure of correctness A B
The assessment of the quality of a surveyor’s work is based in part on the precision of their measured values. Is important for accurate feature representation, analysis, and mapping. When talking about storing data in a geodatabase (single vrs. Double) In the real world (assessment); reality is more a synonym of correctness

11. Application of concept
The best outcome can be obtained by applying a single concept:
Take the best from the experts
Use it to do your job
Share the results

12. Application of concept
Approach used by Mapping:
Registered subdivisions / control points
Parcels (tax parcel base)
High resolution color orthophotos

13. Application of concept
DPW can provide new subdivisions registered to control points

14. Application of concept
The Assessor's assembles the tax parcel base (GIS layer)

15. Application of concept
A consortium can provide other elements

16. Application of concept

17. Application of concept
3,170 ft
5,910 ft
7,490 ft
2,230 ft

18. Application of concept

19. Application of concept

20. Application of concept

21. Application of concept
Now you have an ACCURATE product:
TAX PARCEL GEODATABASE
That can be shared by:
DPW - DRP - ROV - FIRE - SHERIFF
And other local agencies

22. Application of concept

23. the Office of the Assessor
Who do we work for?
Wrong!
The Office of the ASSESSOR, and our primary function is to produce Assessor Maps.
We work AT
the Office of the Assessor
FOR the TAX PAYERS!!!

24. Who do we work for? FAIR and CORRECT valuations,
The TAX PAYER wants and expects:
FAIR and CORRECT valuations,
which comes from us being able to choose between
PRECISION and ACCURACY

25. Who do we work for? ACCOMPLISHMENTS 2,600,000 assessments
Over one TRILLION dollar roll
99.2% accuracy (SBE audit)
Over 25,000 new parcels mapped
AMB pages updated every 2 ½ hrs

26. Questions?
Now... THIS is precision!