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Managing Symbology using Python

DaveJordan1

Can someone point me to the correct help source for managing symbology using python? I want to change symbol colors, line widths... for feature classes as well as graphics

Thanks in advance

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MarceloRosensaft

Hello all,

I'm looking for a solution to my situation although I'm quite pessimistic. I work with Python/arcpy for ArcMap.

I have a similar situation like the one previously described: one huge layer file with the enterprise symbology for a polygons unique value layer and the need to apply it to smaller layers programatically. I use Python and arcpy.mapping since I need MXD files, although a solution for arcpy.mp would do some help.

I tried ApplySymbologyFromLayer_management and also mapping.UpdateLayer. Both work by creating a layer that can be saved to a layer file and also saved in an MXD. The problem is that my value field values are not ordered in the order that I want to see in the TOC - the order that we use in the symbology of the enterprise layer file - and when I use any of the two methods - ApplySymbology... or UpdateLayer - I get the values list in ascending order of the value field and that's not what I need.

I've also tried to play with the symbology.classValues and symbology.classLabels lists, by changing the order of the elements, but nothing helps. The order goes back to the wrong one.

I'm happy with any help. Thank you in advance,

Marcelo

RPH_Getech

All,

Hopefully this is of help to some of the folk above, or those who arrive at this thread via google or the ESRI search.

We have had similar issues to those detailed above. We have a corporate style file, and multiple datasets which we need to generate representations for, whereby we only require the unique symbols pertinent to each layer to be saved in the representation.

Having generated a layer file based on the entire style file (by "matching to symbols in a style") we were frustrated that the "apply symbology from layer" command wasn't dynamic, i.e. it generated lots of redundant symbols that weren't present in each dataset. Especially as the help file implies it is dynamic...

Esri Apply Symbology Help

Much experimentation led me to the conclusion that it is dynamic, just not when you have matched to symbols in a style. Changing the layer file to a "Unique Values" list enables the dynamic functionality!

Rather annoyingly, if you match the symbols first, and then switch to a unique values, your layer file will retain the symbology, but once again you won't be able to dynamically match to it.

Therefore, the workaround is to manually create a layer file (hopefully you only need to do this once), from scratch, with all of your symbols and labels as you would like them as a "Unique Values" list (you can speed this lengthy process up by loading your style file into your Style Manager). Save it and then reference that using the "apply symbology from layer" command.

You then have a way of dynamically updating symbology for multiple layers containing different subsets of features.

BrandonConner

Sorry, ApplySymbologyFromLayer_management() doesn't respect the headings in the layer file, so it still has to be edited. That's actually worse than deleting all the values with a zero count when using mapping.UpdateLayer().

Thanks for trying though.

JasonHarshman

What if you used Make Feature Layer on the layer file source, but dynamically apply a where clause to only the feature(s) in a given feature class. Then use ApplySymbologyFromLayer_management to apply the symbology to the feature class from the temporary layer created using Make Feature Layer. Something like this:


sourceLyr = "source_layer.lyr"
tmpLyrName = "tmpLyr"
featureClass = "data.gdb/fc"
expression = some SQL 

MakeFeatureLayer_management(sourceLyr,tmpLyr,expression)
ApplySymbologyFromLayer_management(featureClass,tmpLyr)

It seems what you're trying to do can be done without manually editing so I'm sure there are probably other ways to do this.

BrandonConner

It's not that I can't find a way to display them.

These layer files are converted to kml's and ovl's. They get delivered to customers.

Not GIS expert customers either. My main customer is the NAVY.

I've python scripted most of the final product creation that we do here, but this last thing still has to be done by hand.

JasonHarshman

Can you set the legend option to "Only show features class that are visible in the current map extent"?

BrandonConner

I have a situation where I have a unique values source layer file that I use to update polygon feature classes with the appropriate symbology.

arcpy.mapping.UpdateLayer() does a great job, however, it applies all possible values ( 428 possibles ). This makes the legend unusable, and I only need the 10-20 I actually have values for in the feature class. Using the symbology.addAllValues() changes my labels AND reorders the colors assigned to the unique values, frustrating.

arcpy.ApplySymbologyFromLayer_management() only applies the ones I have values for in the feature class, fantastic, except it doesn't respect the headings from the source layer file. What do I do?

Do I edit each layer file I'm creating to add in the headings, etc... that I need? OR

Do I open each layer file and delete all values that have a zero count?

Keeping in mind that there are many of these files generated daily.

Thanks for your time and any offer of help,

Brandon

ColinLang

Here's a real world example:
   We used to do this process in VBA, but as support for VBA is being dropped from ArcGIS, we were trying to transition to python.
   We are creating a series of maps that give instructions to operators flushing out a town's water system. We have 300 fields in the data for pipes, hydrants, valves, etc. Each of those fields can essentially have a value saying whether the item was used in a previous route, is used in the current route or has not yet been used in a route. Linear referencing doesn't work for this, because for most routes, there are branch pipes off the main that get flushed by water going up them and back - ie. follow a branch till the first valve. So as we do the data driven pages or python mapbook, we constantly change which field the symbolization comes from. In ArcMap, when you apply symbolization from another layer you can choose which field to apply that to, but the same command in Arcpy limits you to using the same field name. So we tried to change the field name using lyr.symbology.valueField but that eliminates all the symbols. We can re-add by using the .addAllValues function, but these then show up with default symbolization, with no way to control it. So it looks like all the effort I put into my python scripting is now a waste, because I can't control the symbolization. In the end the script was going to generate both mxd's and pdf's in case there was any required tweaking to the route maps, so Data Driven Pages just doesn't cut it.

   To control my symbols with layer files, I need 5 layer files per route - one each for pipes, hydrants, stand pipes, drainage outlets and valves. For 300 routes in a small town that's 1500 layer files. I'd hate to do a city.

   I even opened a layer file in a text editor, to see if I could manipulate it on the fly but it's mostly machine code - very little english text.

RichardFairhurst

Hi Jeff - I stumbled across this forum post while researching a workaround to your 'line in the sand'. I need to generate approx 30,000 point feature classes and then render each one with a unique combination of CMYK values. Due to the size of this project, automation is the only solution however, the symbology properties exposed through the arcpy.mapping module are SO limited...the solution offered is to hit against a .lyr file that has been pre-generate with the exact CMYK combo I need. If I have to go through the trouble of generating all the .lyr files, i might as well just symbolize each point layer by hand. Ideally, exposing the RGB, HSV, or CMYK values would be EXTREMELY valuable in this instance as I'm sure in so many others. I don' have time to go the ArcObjects route...what do you suggest?

Thank you.

30,000 symbols distinguished only by color is a questionable cartographic design in my opinion. What could a viewer possibly gain from the resulting set of thousands of indistinguishable symbols generated on that order? I could see the point if these were sign faces or more complex than mere color gradations, but if does not sound like that is what you are aiming for. I do not see the value in a symbol set like that unless you have some justification for this design that escapes me.

In any case, I would argue that you do have the time to do the ArcObject route if you are determined to do this, given the amount of time you would save by avoiding a manual solution. Waiting for arcpy.mapping to support this option would require you to wait much longer for this solution and involve a much greater effort on ESRI's part than your writing the code in ArcObjects using the forum help already available on this subject. It is not like ESRI has given you no alternative to a manual approach and from a cost benefit perspective, I would say you have clearly reached the point where .Net/ArcObjects is your best route. ArcObjects is EXTREMELY valuable in this instance.

Arcpy suffers far more limitations than users who only attempt to learn that will ever know. I have had to abandon supported arcpy functionality in favor of ArcObjects on several projects due to performance requirements that I could not overcome with arcpy. Arcpy has its place, but ArcObjects will always be superior to arcpy on several fundamental levels from my perspective and encouraging people who want to push those limits to stay with arcpy is ultimately a disservice.

RebeccaRothbard

Hi Jeff - I stumbled across this forum post while researching a workaround to your 'line in the sand'. I need to generate approx 30,000 point feature classes and then render each one with a unique combination of CMYK values. Due to the size of this project, automation is the only solution however, the symbology properties exposed through the arcpy.mapping module are SO limited...the solution offered is to hit against a .lyr file that has been pre-generate with the exact CMYK combo I need. If I have to go through the trouble of generating all the .lyr files, i might as well just symbolize each point layer by hand. Ideally, exposing the RGB, HSV, or CMYK values would be EXTREMELY valuable in this instance as I'm sure in so many others. I don' have time to go the ArcObjects route...what do you suggest?

Thank you.

BrianHall1

I have a related but even simpler issue with the UpdateLayer process in python.

I am making ~130 thumbnail map showing New England towns (~2000 town) and I want the polygon outlines to be thin...around 0.10 pts.

I make my source_layer have thinner outlines, but whenever arcpy does the UpdateLayer function, they come back with 0.40 widths. This happens even if I sent the outline on my source_layer to no outline/no color.

-Brian

jbarrette

I think I understand your requirement. You want your fill symbol angles to always align with the page, not the data. For example if you have a 45 degree cross-hatch symbol and a rotation = 0. Then then both the legend and the cross-hatch symbols are at 45 degrees. If you rotate your data frame 10 degrees, the cross-hatch symbols also rotate 10 degrees (but the legend does NOT). So you have to go into your layer, symbology properties and set the fill angle property to be 35 degrees.

The only way I can think of doing this with arcpy.mapping is if you have a limited number of rotation angles. I would author a layer file for each possible rotation and modify the fill angle property. As I go from page to page to page, when setting data frame rotation to a non-zero value, I would update all the appropriate layers with symbology from the matching layer files.

I know its a work around but it can work for now.

Thanks for defining this requirement.
Jeff

TedChapin

Jeff,

Hopefully you still get a notification of this reply to a year-old post. Here's a real-world scenario where sheet-by-sheet programmatic access to detailed symbology properties is needed. Data driven pages support attribute-driven map rotation. But polygon line fill symbols do not support attribute-driven angles. So when the data frame is rotated the 45 degree symbol is not 45 degrees anymore. This is a real problem if you have more than one angled line symbol (forward leaning angle means one thing, backwards leaning angle means something else). If the map is rotated just right the symbols are just cartographically wrong. In a static map you can calculate the fill angle to compensate for the map rotation, but this is not possible in a dynamic data driven page where the rotation is changing. We can do really cool things with Python and data driven pages, but this is not one of them. ArcObjects should not be required to solve this problem, which has existed for years.

Ted Chapin

MatthewGerbrandt

Hello, everyone. I'm a little late to the discussion but was hoping one of you could point me in the right direction. I've got a script that downloads a large number of shapefiles from an FTP site.

Those shapefiles are then imported into a FileGeodatabase FeatureClass and their datestamp is used for graphically differentiating them. These datestamps change over time, so three days from now, thousands of new datestamps will appear in the database. I want all of these data to be represented by a an arrow whose rotation is defined by a field in the featureclass. I've attached a screenshot, showing the conversion which I need to perform in terms of symbology.

Could someone please tell me if this task is possible through Python and if so, how would I do it? Thanks a million!

I'm the guilty one, that was my presentation and my quote. Now I want to give it some context and ask a couple of questions...

Help me understand, in a real mapping scenario, why do you need to dynamically change these symbol properties?...

I'm not trying to argue here, I'm looking for well documented scenarios to help us continue expanding the capabilities of arcpy.mapping where absolutely needed for map automation tasks. At 10.1, we added quite a few new capabilities including some symbology classes that are needed to support map automation: GraduatedColorSymbology, GraduatedSymbolsSymbology, etc.

Thanks for your help,
Jeff

Screenshot.JPG

BarraLoubna

Hello,

I would like to change the symbology of a single layer at a transition from one scale to another.

You can found my post here:

http://forums.arcgis.com/threads/72035-How-to-change-the-symbology-of-a-single-layer-at-a-transition-from-one-scale-to-anoth.

Please i need a help.

Thank you.

ChristopherThompson

I'm the guilty one, that was my presentation and my quote. Now I want to give it some context and ask a couple of questions....We could easily triple the arcpy.mapping API but just attempting to provide all that capability. We don't want to do that. We are trying to keep arcpy.mapping as simple as possible without making it as complex as ArcObjects....Help me understand, in a real mapping scenario, why do you need to dynamically change these symbol properties? ...without having to recreate ArcObjects capabilities at the arcpy.mapping level...Thanks for your help,
Jeff

Hi Jeff, don't misunderstand me, i totally get the message and understand why there are limitations in the arcpy.mapping module. I'm really on the fence with some of these issues. As a user in a real-world GIS context the issues surrounding my desire to have more ability within arcpy.mapping are two-fold.

One is simply about having tools that are easily grasped and are accessible. ArcObjects is great, if you are writing .net code and have access to development tools like VisualStudio - but not all organizations have these or the staff who have the skills to use these. The amount of learning one has to do to master ArcObjects is also somewhat formidable as well, and given the rate at which technology is advancing, the more things one has to learn to simply 'do the job' is a challenge. I love Python because it cheap, fast, easy and lightweight (attributes i tend to appreciate about most things in life) - it costs virtually nothing for my organization to use and the ease of which it can be implemented really helps in the fast-paced world in which we tend to work. Conversely, I also don't want to see arcpy.mapping become so bloated and complex that it defeats the stated purpose. Part of my 'frustration' (if you can call it that) is that VBA is gone- Python scripting I thought was the answer to the deprecation of that capability, but arcpy and arcpy.mapping does that in a hamstrung way. At least with VBA you had access to all of arcObjects, even though you can't really distribute those tools very easily.

The other issue simply has to do with real world practicalities of managing things like .lyr files. So much of what we do are short lived products that managing on-disk libraries of things like .lyr files and such just isn't always practical. If i can write code that creates these without having to take the time to create and maintain a file structure and things inside it then thats very helpful. For example, recently i wrote a script that makes a selection in featureclass A, and then selects all features from another featureclass B where those features intersect. The outputs from the script are .lyr files saved to disk with definition queries so these aren't simply 'selection layers'. How nice would it be to simply create those layers on the fly (there are 96 of them in the end) and add those to maps iteratively and apply symbology. To accomplish this in arcypy i have to save these to disk, manually create 'template layers' with the proper symbology (simple stuff like line weights and color), then write the code to access those .lyr files and point at the template layers to get symbology, and then add those to a map. Though its easier than doing this manually, its certainly not as elegant as it could be and having to write data to disk seems unnecessary.

Ultimately, things aren't bad, they are in fact really good, its just the more capability I see, the more I want without having to change horses. I want one set of development tools, and not have to spend time moving down one development path only to realize "oh crap, i really need to be writing .net code against arcObjects to do this". Contact me via email if you want to discuss more about some of this - i dont' want to take this thread any further off-topic at this point.

jbarrette

I'm the guilty one, that was my presentation and my quote. Now I want to give it some context and ask a couple of questions.

Authoring symbology in ArcMap is a simple process but think of all the possibilities and all the options available via the symbology properties dialog. We could easily triple the arcpy.mapping API but just attempting to provide all that capability. We don't want to do that. We are trying to keep arcpy.mapping as simple as possible without making it as complex as ArcObjects. Do you just want to change the color ( should we include RGB, CMYK options), or will you also want to change the symbol size, outline width, pattern, etc, etc? That was the point of attempting to draw the line in the sand between what is pure map automation and what can be done with ArcObjects.

Help me understand, in a real mapping scenario, why do you need to dynamically change these symbol properties? Why does the color/size of a layer need to change going from map sheet to map sheet? If the point is to update the color for a layer in many map documents across a system, then UpdateLayer along with a layer file works really well (without having to recreate ArcObjects capabilities at the arcpy.mapping level).

I'm not trying to argue here, I'm looking for well documented scenarios to help us continue expanding the capabilities of arcpy.mapping where absolutely needed for map automation tasks. At 10.1, we added quite a few new capabilities including some symbology classes that are needed to support map automation: GraduatedColorSymbology, GraduatedSymbolsSymbology, etc.

Thanks for your help,
Jeff

ChristopherThompson

Here is a quote from a presentation from ESRI about map automation using python:
"This is not a replacement for ArcObjects â?? we are trying to draw a line in the sand"
Clearly, the powers that be at ESRI want you to do something as 'advanced' as changing basic symbology (like point sizes and lineweights, colors, etc.) by using ArcObjects. The updateLayer method referencing an existing .lyr maybe your best bet. Just another somewhat annoying thing, like having to create a .lyr file before you can add a layer to a map document.

GIS1

Hi Ubanide,

I know what you mean.

Though I do not have a solution and haven't figured out how to do what you want (I wouldn't mind knowing), I can tell you how we do it. We simply make layer .lyr files with the symbology we want already customized and save them to our network drive. Then we just use those in our scripts to apply symbology from them. Might be a workaround for you if you can't figure out how to do it your way.

Best of luck!

WilliamIde

All I want to do is to change the size and color of the points in a layer file. Easy to do in Arcmap. Impossible in arcpy?
Shouldn't be.

jbarrette

I can not reproduce this. I've tried updating with layers from layer files, other MXDs (as in your example), I've done with with stand alone scripts, using CURRENT, etc.

Please provide more detailed steps so I can evaluate this further.

Thanks,
Jeff

ThaiTruong

I just skim through the functions and classes under arcpy site package from the help file, yet could not find any methods to manipulate the symbology either. The only way I can do this is to apply the symbology to my new feature class from another existing layer using "gp.applysymbologyfromlayer".

Here's the link:
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00170000006n000000

DaveJordan1

jaybo684 - I still don't have a solution for this issue. In fact, when I received notification that you had commented on this post, I was looking at the same issue generated from a Flex widget...

JasonHarshman

I'm having the exact same problem. If the original polygon symbology is hallowed or outlined, then the script will fill the polygon with black. However, if I open or import the layer file within ArcMap the proper symbology is displayed. I haven't tried it with points or polyline features yet.

DaveJordan1

I found this sample code for UdateLayer (using a .lyr file). However, I used a No Color option in the .lyr file but it comes in solid Black!!!:

import arcpy

#Reference layer in secondary map document
mxd2 = arcpy.mapping.MapDocument(r"C:\Project\ProjectTemplate.mxd")
df2 = arcpy.mapping.ListDataFrames(mxd2, "Layers")[0]
sourceLayer = arcpy.mapping.ListLayers(mxd2, "Rivers Group Layer", df2)[0]

#Update layer in primary map document
mxd = arcpy.mapping.MapDocument(r"C:\Project\Project.mxd")
df = arcpy.mapping.ListDataFrames(mxd, "County Maps")[0]
updateLayer = arcpy.mapping.ListLayers(mxd, "Rivers", df)[0]
arcpy.mapping.UpdateLayer(df, updateLayer, sourceLayer, False)

#Save to a new map document and clear variable references
mxd.saveACopy(r"C:\Project\Project2.mxd")
del mxd, mxd2

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