Latest Contributions by wusirui

Hello Thank you for your good presentation! I think this is a good way. But should I calculate the area of each polygon before working with Spatial join? Because I need compare their area. ... View more

Like what you said, I want to check how much it overlap each other and how it correlated (etc, one to one or one to many? or many to one?)I want to check how many polygons are matched from layer A to layer B and how. Here , taking a simply example as following (A1, A2,A3, B1,B2,B3 are polygons) Layer A (#30000: number of polygon) :                 A1                 A2                 A3 Layer B: (#70000) :                B1                B2                B3 Because Layer A and Layer B are working with same region so that they have almost same city shape but their areas are different. That is, these two layers are somewhat different, which means A1 might not completely corresponding to B1. In this example, B1 might contain the sum of A1, A2, A3..... because layer B has more polygons (please note Layer A and Layer B are in same location). So, what I am going to do is knowing how do these two layer correlate each other (in terms of its city'area). ... View more

Hello Riyas I know that Union function can combine these two polygon files and obtain a new overlay area. But, do you have any idea how can area parameter can be correlated? I want to check thier spatial correlation. Thank you for your reply. ... View more

Hello I suggest that you could search some scientific papers and decide one direction that you want to work with. It is hard to say how does flood map can be defined. That is, You need to know what you need and how to get it.  You could search related scientific papers in Google scholar and may get some ideas about how you can get your flood maps. In my opinion, Flood map refers to many directions and points, such as how we can define Flood map? how flood map can be mapped and how we can measure this flooding. So, just get this macro principle and then you will know what kinds of process you need to work with. Of course DEM data, flow direction and accumulation and stream network should be very helpful. Also, there were many tiny but important things during your processing, For example, How can you define your accumulation threshold and why this is important? So, read more papers and then you could focus on your technique part. ... View more

1.  If it came from two independent sources it cannot be precisely aligned.  Even a single source agency may be sloppy with this kind of topology.  The different numbers from the methods you used show it is bad topologically. 2,  The two methods are not equal.  Polygons are harder to edge match than a it is to locate a point in the correct surrounding related polygon.  One polygon equals one point regardless of size, so a single feature would never generate 2 points.  The only question arises for multi-part polygons.  If you break a multi-part poiygon into separate singlepart polygons then you have to track the source city ID for a count.  In general extracting a single points with the inside option is all you normally would need, unless you have very gerrymandered boundaries. 4.    The points method is my preferred method, but it requires an Advanced license, so other options have to be applied if you have the Basic or Standard license levels. Sorry, I forget one thing. You said Integrate function can help correct the features but how to set this function in ArcGIS. For example ,Should I input these two features together or put it separately. ... View more

1.  If it came from two independent sources it cannot be precisely aligned.  Even a single source agency may be sloppy with this kind of topology.  The different numbers from the methods you used show it is bad topologically. 2,  The two methods are not equal.  Polygons are harder to edge match than a it is to locate a point in the correct surrounding related polygon.  One polygon equals one point regardless of size, so a single feature would never generate 2 points.  The only question arises for multi-part polygons.  If you break a multi-part poiygon into separate singlepart polygons then you have to track the source city ID for a count.  In general extracting a single points with the inside option is all you normally would need, unless you have very gerrymandered boundaries. 4.    The points method is my preferred method, but it requires an Advanced license, so other options have to be applied if you have the Basic or Standard license levels. Ok, I will try and hope this can be helpful. Thank you ... View more

None of them are accurate.  The two source maps will not match boundaries exactly where the two sources touch boundaries and as a result none of these methods will return a true answer.  If the boundaries matched without crossing, then probably all methods would yield the same result.  So the critical item is boundary alignment.  As long as boundaries cross each other, Spatial Join is under-counting when you use the Contains option, while Union and Clip are over-counting small slivers of polygons. I would make copies of the source feature classes and use Integrate on them first to align the boundaries together better, then try the Spatial Join option with Contains.  The number will likely increase.  (Be sure to do Integrate on copies, not the original, since it directly alters the source geometry.  You should always maintain an unaltered version of your original data unless the edits are verified before destroying the originals.) However, the real method I would use with an Advanced license is to first use the Feature to Point tool to extract the Inside point option of each city and then use Spatial Join to the points.  Then use an attribute join of the points to the city polygons to transfer the country attribute.  I might test the Multipart to Singlepart tool option before extracting the points to ensure they were centered inside each separate polygon part prior to doing the join and then performing a Summary Statistics to verify that each part fell in only one country before doing the join.  If they did I would do the transfer.  If they didn't, I would examine each that had a different Min and Max Country ID to find out how bad the overlap was affecting them. Getting exact counts is one of the most difficult tasks when data is poorly aligned.  Several validation steps have to be done to verify that you have a correct result and manual intervention is almost always needed when the boundary alignment is very poor. Hello Sir Thank you for your kindly answers and suggestion. I also have some further questions regarding to your answers. 1. How do you know if one data is porrly aligned? Does this always happen or it is common? 2. You mentioned two methods to check, one was Integrate and another was transform polygon to points. Were these two are equal? if polygons are transformed to be points, do these point are reliable? For example, one big polygon might be split as two points then the number of cities (here is number of points) would increase. 4. I dont care if those points layer cannot be retun to be polygon since the only thing I need to know is How many cities are located in different countries. Which methods you prefer? This is very important to me and thank you for your kindly help. ... View more

Yes, instead of getting the statistics interactively, you can use the Summary Statistics tool Yes, that tool produces an output table. Yes, you have to look up the value of the MEAN for the field on which you requested statistics. A search cursor will do that quickly (there will only be one record). If you assign the value you have plucked from the table to a variable, you can use it in the subsequent where clause. You never mentioned using model builder before, so I gave you the interactive workflow. A Model Builder workflow will mirror the interactive one. Hello. Sorry for my miss mentioned. Could you please give me a simple example of how can that output mean value was defined or linked? if this is possible. Thank you ❤️ ... View more

To get the average line length interactively, right click on the Shape_Length field in the attribute table and click statistics. let's say, for example, that the average is 5000 meters then you create a feature layer of the lines feature class, with a where clause: "Shape_Length" < 5000 You can make the layer interactively in ArcMap by adding that statement above as a Query Definition to the layer, or inside or outside of ArcMap by using the Make Feature layer tool and setting the statement as the where clause or Expression Now use the layer as the input to Feature To Polygon Only the lines of less than the average length (in our example, 5000 meters) will be used by the tool. Hello, I have a further question. You said the mean value was calculated by clicking stastisic. however, in modelbuilder, summary stastastisic can only calculate mean value through output a new table file. How can I connect to this table file? In my case, mean value is not a number rather it is a variable. for example, Shape_Length < table.mean (5000, 4000, 8000?). So.if it is possible to define mean value in table field? then this mean value can be used as a variable in Query definition? ... View more