# GeoCoding QGIS plugins

I perform manual linear referencing (geocoding) on a daily basis.

The area I do this for is large. Because of this, a consultant was hired to study the region and develop a grid some time ago that we could use to assign a min and max to the endpoints of roads; also incorporating orientation of the civic address on the road (north/south vs east/west side)

You will need a policy or some guidelines to go by.

For example, when it comes to road orientation, we first look at the roads orientation: is it travelling north/south or east/west?

Then we look at the side of the road that the new address is: on the west/east side or north/south side.

From those two, we can decide whether or not the new number is going to be even or odd!

The guiding chart we use:
West/North side of road = EVEN
East/South side of road = ODD

Now you need to have someway of giving the min and max... Like I said, for our case, we have a grid to use and depending on where the road intersects the grid, that is the assigned min and max.

We also assign the new number based on where the driveway intersects the nearest public road.

There are two methods that I mostly use. One involves using existing house numbers as a reference to get the new number and the other involves using the 'reference grid'.

• Method 1) Using existing house numbers:

In the following image
- houses 1465 and 1592 are the closest (being on either side of the new house), so I start with those where:
h1 = 1465, h2 = 1592 and...
d1 = "distance from h1 to new house", d2 = "distance from h2 to new house"...
which would look like:
( ((h2-h1)/(d2 + d1)) * d1 ) + h1 -> ( ((1592-1465)/(510m+156m)) * 156 ) + 1465
= ( (127/666) * 156 ) + 1465
= 1494.8 (+/-1 to round and make even or odd...)
= 1494!

Note, that above, when I measure along the road, I am measuring where those houses driveways meet the road, NOT the distance between the physical location of the house!

• Method 2) Using the 'reference grid':

First measure the total length of one reference grid to the other.

In the image, we need to measure from West 1600 to West 1400 (r1) (off the map) which gives us a total of 2800m (d2) .

This is HUGE! Usually I deal with a smaller distance of around 500-1000m.

Also get the difference between the two grid lines you measured, so 1600-1400 = 200 (d1) !

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### Probably Tiger Line

by navel

The US Census has a free database called TigerLine. It's not always accurate. I've worked with it and field surveyed some glaring anomalies.
Now, I'm not sure MapQuest and MSN Maps are derived from TigerLine, but chances are they are. I recall researching some commercial geocoding services that purportedly enhance the accuracy of TigerLine.
If you email me your address, I could check the TigerLine for the bay area and see if the anomaly you noticed correlates.
If you're in the Castro or UpperMarket, I could help you with a very accurate map. My maps are based on the San Franciso GIS Department's CAD maps.

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