topic Re: Spatial reference does not match data frame in Data Management Questions

Spatial reference does not match data frame

RobertStevens — Mon, 04 Apr 2016 05:43:11 GMT

Can someone answer this question. It is not peculiar to any version of Arcmap desktop: I have seen it in 10.0, 10.1,10.2,10.3 and 10.4.

When I "start editing" from the editor toolbar I get a dialogue box asking which layer or workspace I wish to edit.

After I choose one I get another warning dialogue box which lists all (well, all, as far as I can tell) the layers in the frame and where each one has a message "Spatial reference does not match data frame". There are many layers in my frames because I am using Business Analyst basemaps which have multiple datasets which display at different scale values.

Why do I get this message? Both the data frame and the layers are using the same geographic coordinate system (WGS_84), although the former is projecting the data using the World Mercator projection.

The warnings don't prevent my being able to edit the data: I am only editing fields which are not geographic. But the message seems to imply that if I were digitizing new features that I would be met with failure.

Re: Spatial reference does not match data frame

NeilAyres — Mon, 04 Apr 2016 06:06:33 GMT

It's just a warning. Telling you that it is probably wiser to edit the spatial data in the same coordinate system as the data itself.

Re: Spatial reference does not match data frame

DanPatterson_Retired — Mon, 04 Apr 2016 07:44:54 GMT

This will become important if you decide to create data because you may end up with a file in Web Mercator instead of GCS WGS 84, which I presume, is the coordinate system that you would prefer to keep all you data in

Re: Spatial reference does not match data frame

RobertStevens — Thu, 07 Apr 2016 19:24:12 GMT

Ty for responses Neil and Dan.

Dan, are you saying that if I created new features (I am not BTW), that

those new features would change the coordinate system of

the underlying dataset?

Ie: I have features with GCS WGS 84 coordinates. I have a map

with world mercator projection. I create a new feature, and

the coordinates are stored in meters in the original dataset?

So I have umpteen features stored as a pair of angles, and

one feature stored with a pair of huge numbers?

Or is it rather that the new feature will cause all the values

in the original dataset to be converted to meters, and

the coordinate system description will become Web Mercator

(which I wouldn't want since I had a reason for having the

original dataset in CGS WGS 84)

Re: Spatial reference does not match data frame

DanPatterson_Retired — Thu, 07 Apr 2016 19:37:52 GMT

Nothing changes the coordinate system of something that has been started and the edited again. I said new features as in a new feature class or shapefile. I have seen way too many times that the difference between the data frame and desired coordinate system has led to hours of confusion. Just be aware of the rules and the safest rule is never to mix coordinate systems. I always go the extra mile and standardize the data to one coordinate system. This unfortunately doesn't work for people forced to work with web-based basemaps and the like. They have to be more vigilant.

Re: Spatial reference does not match data frame

RickGeittmann — Thu, 07 Apr 2016 23:23:14 GMT

It would appear that the data is reprojecting on the fly from WGS84 to Web Mercator.

I would not edit the data in this case if my statement above is correct - editing in this manner will most likely induce errors into your data.

Remember the first data element added to a ArcMap session sets the data frame reference for the coordinate system unless someone manually set the coordinate reference first then brought the data in.

Information: Spatial reference does not match data frame—Help | ArcGIS for Desktop

Re: Spatial reference does not match data frame

NeilAyres — Fri, 08 Apr 2016 14:53:56 GMT

What is your reason for having the data frame in Web Mercator? Because it's only purpose, as far as I can see, is to be able to display web maps of the world. So it is not very good at scale or area (or anything else projection related). So your decision the have your base data in GCS_WGS84 is fine. Nothing will happen to that, even if your df is set to Web Mercator. The data will still be captured in the coord sys of the source. As Dan says, this can cause confusion, if a user starts edit a new dataset but is not aware of the coordinate system that they are looking at.

And a picky point to Rick...

Data is never IN WGS84. Because WGS84, by itself, is not a coordinate system. It is a datum, geoid & ellipsoid, but not a coordinate system.

GCS_WGS84 is a coordinate system, geographic coordinates based on the WGS84 datum.

Could have many multitudes of other coordinate systems, UTM, State plane, zillions of others, all based on the underlying WGS84 datum.

I have lots of experience with data based on various "classical" datums. Then you need a "transformation" between the two.

Remember, it's ON not IN.

Re: Spatial reference does not match data frame

RickGeittmann — Fri, 08 Apr 2016 15:42:04 GMT

Neil - good point on the WGS84 I should have been specific and not used a general catch all for terminology and confuse folks.

We use the Web Mercator in the data frames for any data that is used in online mapping applications and transform the data to Web Mercator into a DB set up to serve our online applications to prevent the slow down of transforming the data on the fly for the online apps or real time edits resulting in errors from an on the fly transformation.

As Dan Patterson hit the nail on the head in his response.

Re: Spatial reference does not match data frame

RobertStevens — Fri, 08 Apr 2016 16:25:44 GMT

Neil, Rick, and Dan

Thx for these responses: I am learning something from you guys.

Neil asks: "What is your reason for having the data frame in Web Mercator?".

I should have been more accurate and said that the frame is in WGS_1984_Web_Mercator_Auxiliary_Sphere projection (WKID 3857)

Does that change the discussion? But to answer the question: I am using basemaps supplied by Business Analyst.

Those basemaps "choose" WGS_1984_Web_Mercator_Auxiliary_Sphere for me.

(BTW: my area of interest is Portland OR of an area about 30x30 miles, and sometimes a larger area of Oregon, but not the whole state).

Business Analyst (I hope) is supposed to relieve the user of the necessity to worry about such things,

so I suppose I should reflect the question back to ESRI.

Would one of you expert people comment about WGS_1984_Web_Mercator_Auxiliary_Sphere.

And I apologize if, by not specifying the name exactly, I have caused unnecessary work.

Rob Stevens

Re: Spatial reference does not match data frame

NeilAyres — Sun, 10 Apr 2016 15:48:05 GMT

So is the business analyst data coming from an esri online service?

I guess so, since the frame defaults to "Web Mercator".

But for output, do you not switch to your local coordinate system, state plane or whatever it might be?

Re: Spatial reference does not match data frame

RobertStevens — Mon, 11 Apr 2016 18:33:55 GMT

Hi Neil

No, I am using desktop, just on a local machine.

The basemap that ships with Business Analyst displays a map of the whole world, so I suppose

that is why it uses Web Mercator. But an important, perhaps the most important, feature of

BA is that it intended for use by non-GIS professionals (like myself), and hence people who

don't know all the subtleties of projections etc.

There is some history here. BA 10.0 used to use a special projection named, not surprisingly,

"Business Analyst Projection". This projection was described as dynamic. By that was meant

that the details of the projection changed according to the latitude and longitude of the area

of interest, and the bounding rectangle. (Perhaps some guru from ESRI could comment).

It seems that what you are telling me is this. That Web Mercator is essentially never used

as a projection of small areas, distant from the equator. And that, regardless of the

projection used in the basemap as shipped, that it implied that the user would choose

a different projection, better adapted to his geographic area of interest. Im my case

I suppose that would likely be "NAD_1983_HARN_StatePlane_Oregon_North_FIPS_3601",

and that to use Web Mercator Auxiliary Sphere would give a terribly distorted map.

But why doesn't a product like BA make this more explicit for the business user?

Another thing I have never understood about ArcMap is that, if the frame and the

dataset use coordinated base of different geographic datums, it asks the user

for the appropriate transformation to use. Why?? Surely the software itself

is best equipped to answer that question. How am I, the ignorant business user,

supposed to know what the answer to that question is?

Thx for your continuing help.

Rob Stevens

Re: Spatial reference does not match data frame

NeilAyres — Tue, 12 Apr 2016 06:19:47 GMT

On the subject of datum transformations...

If you don't know about projections, then transformations are another whole murky swamp.

The datum, in my way of thinking, defines the location of the origin of the coordinate system relative to a position of the earths surface. We used to have a whole bunch of "classical" datums, those whose primary point is a physical beacon build by geodesists / surveyors in the 18th century. These tie a ellipsoidal model (a flattened sphere) to that point with a known orientation. Everything is measured from that.

Then along came GPS. The WGS84 datum is an ECEF (earth centered, earth fixed). Its origin point is the gravitational centre of the planet.

A transformation is a numerical method to alter the coordinates from one datum to another.

In NAm you have a enormously detailed set of various transformations from your old classical datum (NAD27) to your more modern one (NAD83, which is almost but not quite, the same as WGS84).

The GIS cannot make that choice for you.

But, mostly these days, you wouldn't have to worry about it. Nearly all of your data will already be based upon NAD83 / WGS84 anyway. So no transformation is needed to get the data to align correctly.