Latest Contributions by TOMKONG

Hi, I have a layer of polygons which indicate different census statistical areas. I also have another layer which has buffered around a network of bus routes in the city. I've been playing around with the software but can't quite figure out how to do this. But for each statistical area, I want to calcluate the area within the polygon which is within the buffer layer (i.e. that the buffer layer covers). Can anyone help me with doing this? Thanks 🙂 1.add one new field in the network buffered polygon layer attribute table --called Original_Area, then using calculate geometry to get area value for each polygon (you can transfer this data from Area field also) 2.intersect both layers (census & buffered network) 3. From intersected layer, add one new field - called Percentage, then using Field Calculation to get the Area (intersected area value)/Original_Area (from buffered layer) value that you want. But you need to check the data error and it depends on your source data quality (the network buffering polygons may have overlapping area), and sometimes the result can be changed if you change the buffering distance. ... View more

Hi Tom, I tried your method, but I have a feeling I am defining it improperly.  I exported the shapefile to ASCII using "Export Feature Attribute to ASCII" and made it SPACE delimited.  I then opened it in Notepad and saved it as a .txt file.  Then in Catalog I created the feature class 'From XY Table' and defined the X (Long) and Y (Lat) fields as well as the coordinate system as North Pole Stereographic. I added this into my mxd just to check it out before projecting it to Albers Equal Area (USGS) and let it transform using the 'WGS 84 ITRF00 to NAD 83' transformation on the fly.  It came in far north of my other Albers layers that were already in my mxd.  Any idea what I did wrong? Thanks, Jessie Jessie, If you couldn't match that HRAP layer and your referenced other Albers layers, one of them should be wrong, and you need to check: Set up one new data frame and define its projection as North Pole Stereographic, then bring that HRAP point layer in.   Locate one point to compare the map coordinates (X&Y) if match its coordinates from your source table (your converted txt file).   If it matches, it indicates your referenced other Albers layers' source data is not correct .   Otherwise the point converting  process is wrong, you should check that "define" process--check if the defined projection parameters matches your source HRAP datum parameters . Tom ... View more

It's working as expected.  The default processing extent is the intersection of input extents, change this to union - see the help for more info.  However, any cell with NoData will be NoData in the output.  So change it to a low number first. i.e. in the raster calculator: HighestPosition(Con(IsNull(raster1), -999, raster1), Con(IsNull(raster2), -999, raster2), Con(IsNull(raster3), -999, raster3)) No, the return value of 1 is correct. HighestPosition/Upos returns the position of the raster with the highest value in the list, not the maximum value itself. For your example of 4, 3, 1, 4 is the max and it is at position 1.  For something like 9, 12, 7, the HighestPosition/Upos value would be 2 as the raster with the highest value is at the 2nd position in the list. Thanks for your explanation about HighestPosition output. If the output of the HighestPosition is the number of raster dataset, this function is not suitable for Jproville's purpose, its return is still to be replaced by the ralated dataset cell original value, and to eliminate the "NoData " output value. The Max function is fit this application, but why ESRI removed this tool in the 10 version? ... View more

Thanks lpinner, this was spot-on! In theory it is doing what I need, however in practice it's not working out exactly as planned. I have a follow up question I'm hoping I can get some help with: ... Much appreciated! Did you check that HighestPosition (or Upos) function works well or not? I never use this function, but it seems the illustration from ESRI book is not correct - the return is not always the cell with Max value. ig: the downside left conner cell values from input raster datasets are 4, 3, 1, but the return value for this cell is 1. But the illustration for Max (9 version) function is correct - this cell return value is 4. If the HighestPosition works and your source rasters does't include the 0 value, you can asign the NoData to 0 first; After you get the HighestPosition output, you can asign the 0 value back to NoData (those 0 value celles indicates all input raster datasets are the 0 value in those locations. You don't need to have any value for those celles) . ... View more

My boss has tasked me to take the gridded 2000 Census data, found here: http://sedac.ciesin.columbia.edu/data/set/usgrid-summary-file3-2000  and he wants a lat/long of each point along with its value, and it exported out to a dbf or csv eventually.  He doesn't use ArcGIS......he is an excel guru and loves to analyze statistics through that.  So the way this is broken down is that each attribute of the census has its own file.  You can download it in GeoTiff or ASCII.  Each file is on the same grid, but I see no unique grid cell ID.  Must be internal?  I tried GeoTiff first.  I thought I could use the Raster to Point tool to create points with which to extract data by, but it does not convert the NoData Cells to point.  And since this is grid that I want to reference multiple attributes to the same grid cell, that won't work. I tried downloading the ASCII file, next hoping it would have data visible that the GeoTiff did not.  I viewed it notepad but I doesn't seem to have what I need either, but I'm not sure that I'm viewing it correctly or if I need to calculate anything.  Any help is greatly appreciated. The goal is to eventually do the same thing for the gridded 2010 Census data when it comes out later in 2014.  Then have some comparison.  I checked into doing this myself and asked the person at SEDAC how long he thought it might take.  He said 3 months just for one census year and that was running a cluster of super computers. Yikes! I'll wait! I'm using ArcMap 10.1 with all the extensions such as Spatial Analyst and Geostatistical Analyst.  Service Pack 1. You can reclassify the NoData as one number (ig 555), then you can convert all cells to points, then using ID to join its attribute to point layer. Then using spatial join to join all attribute point layers together. ... View more

Thank you Tom, I see now the benefits of your suggested method. I have extracted the "9"'s and convert to polygon but I cannot find which tool you are suggesting to use to compare two polygonss to find the changes... (I have an ArcInfo license). I would appreciate if you can tell me the name of the tool if possible? Many thanks Ber It's the Symmetrical Difference tool. ... View more

I am trying to transform precipitation data I got from NOAA from HRAP into Albers Equal Area Conic (USGS).  It is an older file (2005) data that is in a point file (grid).  Each point represents the total rainfall (inches) for 2005 for that location. Derived using these methods: http://water.weather.gov/precip/about.php.  There are no transformations available for HRAP.  I even checked the extensive list here to make sure: http://downloads2.esri.com/support/TechArticles/Geographic_Transformations_10.1.pdf I found this about reprojecting it here: http://www.nws.noaa.gov/oh/hrl/distmodel/hrap.htm But this requires an XMRG file, which was not sent to me.  ... Thanks! In my understanding, the ArcGIS couldn't directly read this radar grid data and this data should convert to ASCII then can be read by ArcGIS--using ArcGIS to import it as feature class - when importing it, its projection should be defined as Polar Stereographic (it is not one ellipsoidal earth model but the spherical earth model (datum is simple, only its radius value and one original point). (As that link says the ESRI's spherical radius is little different from the HRAP spherical radius, so after imported to ArcGIS, there should be little distortion produced. The ESRI spherical radium couldn't be modified.) So treat it as normal radar ASCII file (convert to ASCII file first), import it as feature class and define its projection, then reproject it as you want. ... View more

Hi Tom, Many thanks for your reply. I think I may have done something similar - I used raster calculator to subtract each map from my base map to look at the difference between cell values. Do you think the method you suggest will produce different results to what I have done? I see that you have suggested to extract the cells with a value of 9, but i'm still not sure of the difference between the two methods. Many thanks, Ber Ber, In your first post, you said you want to focus on the cells changes that cell with value 9 (suitable for development) and to test the changes affected by different weight models. So the "subtract" you used is only to get the difference between different model cell included all 1-9 values; but the extracting 9 values from different models is to focus on the best area changes affected by different assigning weight values. Tom ... View more

1.Extract the pixcel value with 9 for each overlayed output: raster dataset 1-13, 1 is from base map; 2.Convert the 13 raster outputs to 13 polygon feature classes; 3.Using #1 feature class as base data, and using the Analysis Tool (find the difference tool --ArcInfo license) to find the changes (compair to the base polygon) and unchanges. 4.Then #2.... ... View more

Hi, I am trying to perform something similar...in a way. I want to use the road center line address ranges and according to these values creating a point layer with the address information in them spread throughout the line. Any ideas? I did one project which purpose is to cut the blockside (polygon) based on the street network segs and transfer the street network line seg address to the related blockside. You can: 1.buffer the parcel outline layer (merge outline layer first to make only one line for each side for one parcel) to intersect with the road center lines (merge the centre line based on the road name first); 2.for the intersected line layer and from attribute table to seclect segs that they share the same address from parcel layer and their address road name match the road centre line name from road centre line layer (sometimes one road centre line is intersected with two or more buffered parcel outline polygons, only correct one need to be selected and merging their segs) ... View more

I have a point feature class with a slope as a field value.  I need to create a series of line segments based on the slope value.  For example, I have a point feature class with the following data in the attribute table ID    Slope 1       0.5 2       0.5 3       0.5 4       0.5 5       0.1 6       0.1 7       0.1 My end product would be a line feature class with 2 segments. One segment would go from point:ID 1 to point:ID 4 and the second segment would go from point:ID 5 to point:ID 7 with a gap between 4 and 5 (no line segment).  Any ideas how I can create this? If your source data is raster format, you can convert this grid data to line feature class based on the slope value (seg by slope value) and result will fit to your purpose. (You can join the slop attribute value data back to line feature class). If your source data is in other format (shapfile, geodatabase, Excel table), convert it to grid first then convert the grid to lines in feature class (you need the small cell size setting). ... View more

When you convert the points (from lines) to raster (grid), you can bring one attribute (from points) to raster table and this field can be linked to the line's ID. Point layer can get lines ID (when you convert or after conversion you can join line ID to the point). ... View more

Thank you. I can do the summary statistics but the problem is in the output from the intersect operation. There should not be as many line segements (in 100s of cases they are identical) assigned to each of the buffer polygons as there are. This must be a result of the overlap of the polygons, as it works fine when I use the layer with the contiguous, i.e. non-overlapping land use parcels. In the latter case I get for example 6 line segments if three network links intersect with the parcel (3*2 spatially coincident lines for each travel direction of each link; these are from the model network, hence they have exactly the same location; in the real world, these wold be seperate lanes). If the street street traffic emissions affect both side parcels, that the buffered parcels are overlapped is correct and fit to your puepose; you need to calculate the emissions distribution weight for each parcel (in other word they share that emissions). If you only want assign this seg emissions for one parcel, you need to clean overlapped parcels or using another way to select one seg from overlapping lines. Another thoughts: 1.Clean up the polygon layer first, to eliminate/clean up the gaps between adjcent parcels, overlapped parcel portions, sliver parcels. 2.Buffering the parcel (lot) outlines (one direction) instead of buffering the parcel polygons. 3. You can buffer street network lines instead of buffering parcels (one or two of line directions buffering), then convert the buffered polygons to lines, intersect those lines to parcel polygons. 4.Join the street network attribute data to the parcel layer by using address field, then convert parcel polygons to outlines, select that line closest to the street as target line for this parcel. ... View more