How to QGIS Attribute Table: Selected Feature by Expression tool

hello everyone and welcome back to my channel so in this video i will show you how to use the attribute table select features in qgis so essentially what i'm gonna do is i'm going to get a polygon layer map and then i'm going to use the select feature in qgis to select particular feature with a certain condition that i want so let's just jump right into it so here i have my polygon layer cadastray so i'm just going to open it so here you can see um a catastro layer of lga map in australia and i have made a tutorial video on how to get this data if you're from australia from my previous video but you can use any polygon map that you have if you know how to get the data that you can then use in qgis so here i'm just going to quickly show the i mean change the style so that you can see this more clearly and change the thickness as well so here so what i want to do here is i want to select a certain um lots here if you see these this is the lots that i have in these lga boundary so let's say that i want to choose a lot the lot that has an area of 100 meters squared so if i want to do that in qgs you have to know that the map that you have here it has data behind it and that data is the one that you use to be able to to enable you to select each feature that you want so to do that i can right click here and then i can go to open attribute table so the logic behind what i want to do here if i want to select this feature like um it's like selecting the lots based on the area that i want then here in the attribute map i have to look for the field value that has aria in it but as you can see here in the original file that i have from the government it doesn't have the area attribute here if you see so to to be able to enable me to do what i want i have to get the area attribute first on my table attribute here so to do that in qgis there is this thing called open field calculator which will enable you to generate the area of your map or any shape that you have in qgis if it's a polygon layer so let's say that your shape file is not polygon then you can create a new file a new shape file and then you can copy the previous layer to this new shape file that you have set to polygon because the only way for you to be able to get the area is to have a polygon layer at least for as long as i'm concerned but you can test the other way so here i'll change the decimal number to real and then position to maybe 2 so it's 0.00 and then here under geometry select area and then i can click ok so now if you see in my attribute table here if i scroll down now you see these areas we put and these um this area here um it's not just um of the overall area this area here is the individual area of the lots that i have here in my cadastray um data because this polygon layer here it has um individual polygons so it it's able to get the area individu individually per each lot so next um what i want to do is i want to select only the lot that has around 643 um meter square so if so you can see that the lots that has this big um area here it won't be selected so for me to do that um i can go back to open a trip table here um i'll scroll down here and then you can see this icon here this is to select features using expression so expression here it kind of work like a a code um language well it's not exactly like that but it works in a logic like that so for example here if i want to select the area only the one that is around 643 i can go to fields and values here this is the attributable that i have of this map the property that it has and then scroll down and i can find the area that i have added to my attribute table so i can double click on that and then here this is the condition that i want to be selected from this kadashi so i want an area more than 643 and then if i click select features it selects almost everything in my maps here around 220 000 because um in this condition that i put here it only says select the area more than 643 so it's also select the ariata that has like maybe a thousand meters square but you can see here it doesn't select arias that has less than 643 but this is not what i want i only want um a lot the single lots i don't want the lots that has um big um big uh boundary area like this so what i can do here is i can put a tolerance what i mean by that is i can um calculate like for example i want to get maybe area of 643 with 5 tolerance so five percent of 643 and will be um 675 right so i can double click here again um sorry i can i have to put n here so don't forget to put n there and then i can see i can say n area less than 675 so 675 if is the 5 of 643 after i add five percent to this so if i click select features now you can see that it only selected the six six around six thousand and two hundred and it doesn't select the the big area here so you can see it only selected the the single lots as what i want from this map and then now after i get that um i can close this and then i can go to my layer here and then i can um right click and then i can go to export and then save selected features s so this will only save the selector selected features that i have here so i can go to browse and then i can um yeah i can go to here and i can say um lot selection and then i can unchange the projection as um i have in australia here and then i can click ok i can now just like this now you can see that i have a new shape file only condensed off the lots um the lot selection that i have that i have from the original map here so you can do this um with your map as well um it doesn't have it doesn't always have to be um cadastray um you can you can also explore more on the condition that you can have in expression this is one way to to use the attributable and the selected features that it has in qgis qgis is a really powerful tool you can do um you can do a lot of things using qgis um in terms of analyzing the urban map um having that data if you know how to get the data from your area so this is um so this is the end of it um i hope this is useful for your project [Music]

Channel: Jessica Lupita

Views: 10,601

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Id: vPmHZP9rmr8

Length: 10min 22sec (622 seconds)

Published: Tue Sep 15 2020