map accuracy

[dilbert firestorm]

hey just wondering.

how accurate are these maps with regard to addresses? does it vary from
city to city?

I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.

I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.

I'm also finding its choice of routing strange/odd.

[Dan Wenz]

Post by dilbert firestorm
hey just wondering.
how accurate are these maps with regard to addresses? does it vary from
city to city?
I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.
I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.
I'm also finding its choice of routing strange/odd.

I'm playing with the same (new) model also - no major complaint (yet),
but it tells me I'm home maybe a 100 feet away or so - OK for me, maybe
not close enough for you. There are also options you may have already
noted, fastest route, no or as much as possible major/toll highways, or
shortest route, your choice.

[S. Cargo]

Post by dilbert firestorm
hey just wondering.
how accurate are these maps with regard to addresses? does it vary from
city to city?

I imagine it varies from city to city. It all depends on how accurate
the data was that was submitted to NAVTEQ. (Magellan and Garmin don't
make their own maps... They buy them from a mapping company called NAVTEQ).

Post by dilbert firestorm
I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.
I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.

Not only can map data vary, but the -accuracy- of all GPS units can vary as
well. It all depends on the view of the sky and how many satellites the
unit has a fix on.

If you're on a boat on the flat open sea with the horizon visible 360 degrees
around you, your accuracy will most likely be within 9 feet of your actual
location. If you're on a tree lined street, or on a street lined with
large buildings, your positional accuracy can diminish to 300 feet worse.
Trees and buildings can block the signals from the satellites.

If you have a street with 50 foot house lots, and your positional error
is 300 feet off your real position, then it's quite normal to be 6 houses
away from your programed destination when the GPS says that you have 'arrived'.

Post by dilbert firestorm
I'm also finding its choice of routing strange/odd.

That's normal for all GPS units. They have no idea what streets are... They
just assign numbers to all positions on the face of the earth. Streets are
just a series of positions. Routing is simply a matter of adding and subtracting
positional values.

When you're driving in areas that you know, some of the routes it takes may
seem strange... But it will get you there. This is important if you're in an
area where you have no idea where you're going. The route may not be the same
as a local person would take, but it will get you there.

[dilbert firestorm]

Post by S. Cargo

Post by dilbert firestorm
hey just wondering.
how accurate are these maps with regard to addresses? does it vary from
city to city?

I imagine it varies from city to city. It all depends on how accurate
the data was that was submitted to NAVTEQ. (Magellan and Garmin don't
make their own maps... They buy them from a mapping company called NAVTEQ).

Post by dilbert firestorm
I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.
I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.

Not only can map data vary, but the -accuracy- of all GPS units can vary as
well. It all depends on the view of the sky and how many satellites the
unit has a fix on.
If you're on a boat on the flat open sea with the horizon visible 360 degrees
around you, your accuracy will most likely be within 9 feet of your actual
location. If you're on a tree lined street, or on a street lined with
large buildings, your positional accuracy can diminish to 300 feet worse.
Trees and buildings can block the signals from the satellites.
If you have a street with 50 foot house lots, and your positional error
is 300 feet off your real position, then it's quite normal to be 6 houses
away from your programed destination when the GPS says that you have 'arrived'.

Post by dilbert firestorm
I'm also finding its choice of routing strange/odd.

That's normal for all GPS units. They have no idea what streets are... They
just assign numbers to all positions on the face of the earth. Streets are
just a series of positions. Routing is simply a matter of adding and subtracting
positional values.
When you're driving in areas that you know, some of the routes it takes may
seem strange... But it will get you there. This is important if you're in an
area where you have no idea where you're going. The route may not be the same
as a local person would take, but it will get you there.
aren't the known addresses supposed to be in the map data set? the street names are obviously in the data set, but the location of the numbers aren't.

in this experiment I did over the weekend, I entered a destination
route. The end destination ends in a shopping mall near the expressway,
when the actual address is on a triangle spit of land 50 yards behind
the end destination.

also in another experiment, ended up close to 4 to 6 houses down which
is not bad, but then I'm I'm already looking for the address.

are you sure this is an issue with the GPS tracking, not the map data?

[Gene E. Bloch]

Post by dilbert firestorm
hey just wondering.
how accurate are these maps with regard to addresses? does it vary from
city to city?
I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.
I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.
I'm also finding its choice of routing strange/odd.

It's been a few years since I worked in a mapping company, but what I see
in the current GPS devices makes me think nothing has changed.

The maps do not have exact addresses. They have addresses associated with
the ends of segments - usually intersections. In between, they just do
linear interpolation.

That means if the corners are at, say, 1200 X St and 1300 X St, and you
give 1251 X St, it will put it in the middle of the block, even though the
actual house might be a few dozens of few from there.

They are supposed to know which side is odd and which side is even,
however.

[dilbert firestorm]

Post by Gene E. Bloch

Post by dilbert firestorm
hey just wondering.
how accurate are these maps with regard to addresses? does it vary from
city to city?
I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.
I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.
I'm also finding its choice of routing strange/odd.

It's been a few years since I worked in a mapping company, but what I see
in the current GPS devices makes me think nothing has changed.
The maps do not have exact addresses. They have addresses associated with
the ends of segments - usually intersections. In between, they just do
linear interpolation.
That means if the corners are at, say, 1200 X St and 1300 X St, and you
give 1251 X St, it will put it in the middle of the block, even though the
actual house might be a few dozens of few from there.
They are supposed to know which side is odd and which side is even,
however.

well, that explains it. Guess they don't want to work too hard. :)

[Gene E. Bloch]

Post by dilbert firestorm

Post by Gene E. Bloch

Post by dilbert firestorm
hey just wondering.
how accurate are these maps with regard to addresses? does it vary from
city to city?
I bought a Magellan 1470 gps, a very nice machine. I've been playing
with it this weekend, learning how to use it. I'm a pizza delivery driver.
I'm disappointed in the models accuracy. It got me to the right street,
but as for pinpoint accuracy, it leaves much to be desired.
I'm also finding its choice of routing strange/odd.

It's been a few years since I worked in a mapping company, but what I see
in the current GPS devices makes me think nothing has changed.
The maps do not have exact addresses. They have addresses associated with
the ends of segments - usually intersections. In between, they just do
linear interpolation.
That means if the corners are at, say, 1200 X St and 1300 X St, and you
give 1251 X St, it will put it in the middle of the block, even though the
actual house might be a few dozens of few from there.
They are supposed to know which side is odd and which side is even,
however.

well, that explains it. Guess they don't want to work too hard. :)

There is that :-)

But also, the storage requirements would be immense. You would need a
latitude and longitude and house number for every house on the street, and
you'd have to update that info every time a house is built or razed.

Someone would think of a better way, though - like just house number and
distance from the reference corner (and one bit for side of street).