11.521: Spatial Database Administering and Avant-garde Geographic Advice Systems
11.523: Fundamentals of Spatial Database Management
Due: Tuesday, February 13, 2018
Urban sensing, common computing, and the boundless availability of georeferenced abstracts and geoprocessing accoutrement accept abundantly broadcast the accommodation of burghal planners to observe, analyze, visualize, and archetypal the spatial deployment of people, infrastructure, and amusing and economic action and interactions. While the availability of accordant abstracts has broadcast exponentially, acceptable assay is still adamantine and adapted data affiliation and admiration requires ample abstruse skill, contextual understanding, and adept choices. For any accurate urban planning problem, accordant abstracts are generally abundant (but incomplete), broadcast beyond assorted agencies and sources, and rarely cross-referencable through simple one-to-one relationships. This subject (the full-semester 11.521, and half-semester 11.523) provides hands-on acquaintance with such burghal planning and spatial assay settings using basal GIS and relational database administering accoutrement in a distributed accretion environment.
This lab exercise has two primary purposes: (1) to accustom you with the accretion ambiance and basal GIS and relational database accoutrement that we will be appliance this semester, and (2) to accustom you to relational joins and database queries appliance the structured affair accent (SQL). For many of the 11.523 lab exercises, we use bindle data, sales data, and architecture aisle for East Boston to appraisal and anticipate the spatial aberration in acreage amount and some of the advantage and accessibility characteristics that admission acreage value. Today, we will get started by appliance ArcScene to anticipate the congenital anatomy of East Boston by extruding architecture aisle to the architecture heights that were estimated appliance LIDAR data. Developing advantageous estimates of land amount involves added assay and ciphering back zoning, building type, point-of-interest locations, and added factors can complicate the admiration and visualization. We will get to this in afterwards labs.
If accession abroad has already assembled, cleaned, and cross-referenced all the abstracts and accoutrement that you need, afresh ‘urban analytics’ does not attending too hard. But burghal planners tend to ask questions that accept not already been answered, and abundant of the task involves finding, filtering, manipulating, and amalgamation abstracts acquired from several adapted sources. For abundant datasets, these accomplish crave a added compassionate of abstracts administering tools, location tagging, and abstracts structure. To get started with some of these skills, we will focus on a ‘relational’ abstracts archetypal of affiliated tables and the use of ‘structured affair language’ (SQL) to affair relational databases. For these SQL queries, we will use a set of seven, small tables that are agnate in anatomy and agreeable to the types of advice about acreage buying and acreage use that are maintained by best bounded assessing and planning offices. We will use MS-Access, Excel, and, eventually, PostgresSQL to examine this baby ‘toy’ database of allegorical parcel, zoning, and tax tables.
For those who would like to besom up on your familiarity with ArcGIS, we advance the aboriginal few lab contest from accomplished versions of 11.188 and/or 11.205 or 11.520 (the prerequisites for this course) and/or some of the ‘virtual campus’ tutorials that ESRI provides. The aboriginal two 11.188 lab contest from aftermost Spring are here: Exercise #1: http://mit.edu/11.188/www17/labs/lab1 Exercise #2: http://mit.edu/11.188/www17/labs/lab2 The contest from 11.205 and 11.520 are accessible on Stellar: https://stellar.mit.edu/S/course/11/fa15/11.205/index.htmlYou can admission passwords for the basal campus exercises from the MIT library agents in the GIS lab breadth in Rotch Library. For added advice of GIS abetment from the MIT Libraries see: http://libraries.mit.edu/gis
Additional in-class lab addendum will be accessible here: http://mit.edu/11.521/www/labs/lab1/11.521_day1_notes18.html
For an archetype of a DUSP argument that analyzed voluminous, spatially abundant datasets appliance abounding of the spatial abstracts administering and avant-garde GIS methods abstruse in this class, see Mi Diao’s PhD dissertation, “Sustainable Metropolitan Growth Strategies: Exploring the Role of the Built Environment” (Sept. 2010).
Class Lockers and WinAthena lab machines: We are activity to use our chic and personal arrangement lockers aural the ‘Athena’ amplitude on the andrew arrangement file arrangement (AFS). All abstracts we will use in the aboriginal bisected of the chic (that is, pre-project) will be stored in /afs/athena.mit.edu/course/11/11.521/data. From WinAthena PCs on campus, this chic abstracts locker can be accessed via drive Z: [Navigate the agenda timberline to get to: Z:athena.mit.educourse1111.521data]. For your convenience, you can use Map-network-drive advantage in Windows Explorer to arise the chic locker as drive K:. (Right-click ‘This-PC’ in Windows Explorer and accept ‘map-network-drive’.)
We advance that you save your own appointment on a USB drive or in your claimed Athena locker (which is automatically absorbed as drive I: back you log into the lab machines). The chic contest can additionally be done on your own laptop or desktop computer (both on and off campus) if your apparatus is appropriately configured (with ArcGIS, PostgreSQL, AFS, Kerberos, and – if off campus – a VPN connection). All this software is chargeless for MIT acceptance but the accession can be tricky. We will accommodate instructions and bound abutment for such claimed computer connections.
Running ArcGIS on CRON or WinAthena machines around campus can be acutely apathetic unless you booty accomplish to assure that absence files and datasets are *not* amid on your arrangement locker space. In general, we acclaim that you archetype all data, saved documents, and workspaces to a bounded adamantine drive afore alpha lab exercises. (There will be exceptions afterwards for ample datasets stored in database engines on the net.) Rob Goodspeed (DUSP, PhD student, 2014) wrote a advantageous set of addendum (for 11.205/11.520 a few years ago) that explains how to bureaucracy your workstation to advance the ArcGIS performance. This certificate is accessible via Arch on the class website [https://stellar.mit.edu/S/course/11/fa12/11.205/courseMaterial/topics/topic15/resource/11.520_Setup_Guide/11.520_Setup_Guide.pdf]
and is additionally reproduced, for your convenience, in our chic locker: 11.520_Setup_Guide.pdf
As a warmup for aing week’s ArcGIS contest (in Lab #2), we will appraise East Boston bindle abstracts and building aisle that has been adored in an ‘eboston05’ binder aural the chic abstracts locker.
Copy FROM this binder in the chic locker: Z:athena.mit.edu/course/11/11.521/data/eboston05
Copy TO this bounded drive: C:temp
Within this bounded archetype of the ‘eboston05’ binder is an ArcMap document, eboston05_lab2start.mxd. Double bang on this certificate to accessible ArcMap and amount the East Boston accoutrements and building footprints. Your awning should attending article like this:
The ebos_parcels05 shapefile shows the boundaries of East Boston accoutrements as provided by the Boston Assessing Department for 2005. The ebos_buildings02 shapefile contains the building aisle for East Boston accoutrements as of 2002. The ArcMap table of capacity window additionally shows several MassGIS and ESRI layers that come from ‘web mapping services’ rather than locally stored datasets. These ‘layers’ are images, appropriately scaled and registered to the alike arrangement of the examination window, that accommodate visually useful accomplishments (shade relief) and beginning (symized roads) that help us adapt our East Boston data.
Neither of the East Boston shapefiles contains many attributes – mostly IDs that can be affiliated to added abstracts tables. We will articulation the bindle shapefile to assessing abstracts in aing week’s lab. But the architecture brand shapefile does accept estimates of the ground and roof heights of anniversary building. These estimates were developed from LIDAR abstracts that was adjourned by Homeland Aegis about 2002 and accurate by bounded accompaniment agencies. MassGIS, the accompaniment GIS office, provides downloads of the architecture brand band with the height attributes from their accessible website: http://www.mass.gov/anf/research-and-tech/it-serv-and-support/application-serv/office-of-geographic-information-massgis/
This map document, eboston05_lab2start.mxd, has already adapted the absence ArcMap settings in accordance with Rob Goodspeed’s bureaucracy addendum so that your absence workspace and geodatabase point to folders in C:temp. However, ArcGIS may accept reverted to added defaults if it cannot acquisition the alleged binder and file geodatabase in C:temp. You may appetite to use Rob’s addendum to acclimatize the ArcMap workspace and book geodatabase so they point to places in C:temp (or a bounded USB drive). If you do not, ArcMap operations will be slower than they charge to be back ArcMap will always be annual and autograph acting files into a arrangement drive rather than a bounded drive.
Now let’s use ArcScene to anticipate the East Boston barrio in 3D. Use Start/ArcGIS/ArcScene-10.4.1 to accessible the ArcScene window. Use the ‘Add Data’ figure (or File/add-data card option) to add the ebos_parcels05 and ebos_buildings02 shapefiles into the table of capacity of ArcScene. (You can additionally Drag and Drop the ebos_buildings02 and ebos_parcels05 shapefiles from the ‘Catalog’ window – if it is accessible – into the table of capacity in the ArcScene window.) Accomplish sure that the ebos_buildings02 band is ‘on top of’ the bindle layer. Now right-click the ebos_buildings02 band and accept ‘properties.’ We can bang the ‘Extrusion’ tab and accustom ArcScene to use the roof heights to boot the architecture aisle up to the roof height. Back the arena acme varies beyond East Boston, we should specify the banishment to be [ROOF] – [GND], that is the aberration amid the roof and arena heights. Bang OK afterwards ambience this extrusion announcement and comedy with the decision window to get acclimated to the interface for 3D interaction. Often, users will appetite to amplify the acme to facilitate visualization. You may appetite to displace the banishment to be 5*[ROOF] – [GND] in adjustment to get added height variation. The aftereffect should attending article like this:
This is all that we are activity to do with ArcScene and the East Boston abstracts today. We are a continued way from developing astute architecture and acreage ethics from assessing abstracts and we may also appetite to use a apparent archetypal that does not accept ‘flatland’ for East Boston. Once we accept done added assay to appraisal bindle and architecture ethics we can tag our abstracts with those estimates or generate ‘hot spot’ envelopes that advice anticipate spatial patterns. For now, aloof booty a awning attempt of your ArcScene window and abide that as allotment of your after-effects for this exercise.
In addition, for those who accept not taken 11.188, 11.205 or 11.520, we crave that you complete lab 1 of 11.188 (http://mit.edu/11.188/www17/labs/lab1) and duke in the final blueprint you create. You may additionally appetite to review lab2 of 11.188 – See: afsathena.mit.educourse1111.188www13labslab2lab2.html - which is the aforementioned breadth as: http://mit.edu/11.188/www17/labs/lab2
To facilitate acquirements basal relational database concepts, we will advance a set of seven baby tables that encode land use and buying advice about PARCELS, OWNERS, SALES, FIRES, PERMITS, TAX, and ZONING. This is a ‘toy’ database with alone a few rows in anniversary table but with a table architecture (schema) and ethics that are archetypal of parcel-related abstracts that are maintained by municipalities and counties. An MS-Access adaptation of this database contains the seven tables and is alleged 11.521_lab1.mdb. It is accessible in the chic abstracts locker as 11.521_lab1.mdb (using the older 2002-2006 architecture for MS-Access databases for added compatibility). The breadth of the book in the AFS arrangement book arrangement is /afs/athena.mit.edu/course/11/11.521/data/11.521_lab1.mdb. You can acquisition this database by abyssal bottomward the agenda timberline on Drive Z: to ability Z:athena.mit.educourse1111.521data11.521_lab1.mdb or bottomward the beneath aisle if you accept army the chic locker as Drive K:. You can additionally download and afresh run a archetype of this database by activity to http://mit.edu/11.521/data/11.521_lab1.mdb
Here is an Entity-Relationship diagram of the seven tables (prepared in MS-Access) calm with links to added detailed listings of the entries in the seven tables.
Relationships amid the Seven Tables
The ‘Toy’ Bindle Database
Follow these links for a advertisement of the rows in anniversary table:
FIRES | OWNERS | PARCELS | PERMITS | SALES | TAX | ZONING
For our introductory database affair contest we will use versions of this aforementioned ‘toy’ bindle database stored in adapted formats: the MS-Access database aloof mentioned and one stored in PostgreSQL. Back CRON machines do not accept the apparatus that allows us to administer and advance PostgreSQL tables (pgAdmin), We will admission them from our browser using phpPgAdmin via http://urbansim.mit.edu/phppgadmin. phpPgAdmin is a web-based administering tool that can affix to PostgreSQL appliance a accepted affair language (SQL). Afterwards on, we will use a client-side appliance (pgAdmin) to create, manage, and admission our PostgreSQL tables.
Using MS-Access with the ‘toy’ parcel database
Option 1: (retrieve the database through the file system)
1a. Attach the chic locker as Drive K (as explained above) or cross the AFS folders via Drive Z to acquisition the DATA sub-directory in the chic locker.
1b. Archetype the MS-Access database file, 11.521_lab1.mdb, to about on your bounded drive that is writeable by you. (e.g., C:TEMP). NOTE that, on WinAthena machines, the DESKTOP is NOT stored on a bounded drive but is redirected to your Athena locker (on Drive I:). For the baby ‘toy’ bindle dataset, it will not amount whether you use a absolutely local drive or your Athena locker. However, back we appointment with larger datasets and ArcGIS tools, accepting your abstracts and blemish amplitude on arrangement accumulator will apathetic bottomward the processing and abundantly decrease the believability of the operations.
Option 2: (download the database from a browser)
2a. Enter this web abode into a browser: http://mit.edu/11.521/data/11.521_lab1.mdb
2b. Save the downloaded book to about on your bounded drive that is writeable by you. (e.g., C:TEMP). NOTE that, on WinAthena machines, the DESKTOP is NOT stored on a bounded drive but is redirected to your Athena locker (on Drive I:). Do not accessible the file anon back the browser will save its acting archetype on a network drive by default.
B. Double-click on your bounded copy of 11.521_lab1.mdb to accessible this database book in MS-Access
Once MS-Access opens the database, you may see a aegis warning: “Certain agreeable in the database has been disabled.” This admonishing is because the database contains adored queries that could conceivably be a awful program. Bang ‘options’ and accept ‘enable this content.’
You will see listed in the table of capacity each of the 7 tables listed in the aloft diagram. Double-click on the tables to booty a look. You will additionally acquisition the entity-relationship diagram via the Tools/Relationships menu.
Highlight the ‘Queries’ best beneath ‘objects’ in the capital table-of-contents window and apprehension the two adored queries: q_midsize_parcels and q_parcels_with_fires. If the queries are not listed, left-click the ‘Tables’ branch and accept ‘all access objects.” The aboriginal affair ‘q_midsize_parcels’ uses the accoutrements table to acquisition all accoutrements whose aboveboard footage is amid 10,000 and 100,000 aboveboard feet. The additional affair ‘q_parcels_with_fires’ joins the parcels table to the fires table (using PARCELID) and lists all the parcels that accept had a blaze forth with the blaze date and estimated loss.
Double-click on the aboriginal affair to see the results. Then, accept View/Design to see the GUI for architecture and alteration the query. Also, accept View/SQL to booty a attending at the SQL appearance to see the more-or-less affiliated argument that describes the affair appliance Structured Affair Accent syntax. Do the aforementioned for the added query. SQL is the lingua franca of client-server communication with online database engines and sits beneath the covers of database applications including best web casework and online geoprocessing.
Modify the aboriginal affair to appearance all accoutrements with beneath than 100,000 aboveboard anxiety (not aloof those bigger than 10,000 or with missing data). Modify the additional affair to omit the pid, wpb, add1, and add2 fields and to omit accoutrements whose acreage use is according to ‘R3’.
Cut and adhesive the tables produced by your modified queries into an editor of your choice. Label them appropriately, add your name and them save this argument document. About-face it in as allotment of your Lab #1 exercise.
Using Excel with the ‘toy’ bindle database
You can admission databases adored in MS-Access databases (or in PostgreSQL and added relational database administering systems, such as Oracle) from abounding desktop tools such as Excel
Before aggravating to admission the abstracts from Excel, accomplish a additional bounded archetype of 11.521_lab1.mdb and rename it to lab1.mdb (since some versions of Excel will choke on MS-Access database names with added than 8 characters!).
Open Excel and accept Data/From-Access/Select-Table and baddest MS-Access Database back the chat box opens up. Navigate to your bounded archetype of lab1.mdb and acceptation the ‘parcels’ table from the MS-Access database. [Beware, on earlier version of Excel, that the MS-Query accoutrement acclimated by Excel to interface with the database are fragile. Not alone will they breach if the MS-Access database name is too long, but it will asphyxiate on the aisle name if it contains appropriate characters such as the aeon ‘.’ in 11.521!] When you try to accessible lab1.mdb, you may see a admonishing message, “Microsoft Appointment has articular a abeyant aegis concern.” This is because a awful affairs ability conceivably be bearded as a MS-Access database. You will charge to bang ‘enable’ to get accomplished this bulletin and afresh baddest the MS-Access tables or queries that you ambition to import into MS-Excel. Baddest the ‘parcels’ table.
Use the business cartoon accoutrement of Excel to artifice a bar blueprint assuming the aboveboard anxiety of anniversary bindle in the accoutrements table. Label the blueprint appropriately and accommodate a jpeg, png copy or a pdf book of the blueprint in what you about-face in for lab1. (A PDF book of your exercise after-effects is additionally okay.)
Excel (and MS-Access and ArcGIS) can additionally access abstracts anon from our PostgreSQL server (and best added relational database servers such as SQL Server, Oracle Servers, MySql, etc.). We will use this adequacy in afterwards exercises.
Using phpPgAdmin to run queries on PostgreSQL tables
We do not charge to admission the ‘toy’ dataset from PostgreSQL as allotment of today’s lab exercise. However, the aforementioned seven tables are stored in a PostgreSQL database engine online and we will use this database agent (with abundant larger tables) afterwards in the semester. Here are the accomplish bare to connect to our PostgreSQL database agent appliance phpPgAdmin from any browser on WinAthena computers in our lab (Room W31-301) or from added CRON machines active Windows/Mac/Ubuntu (or from any added device affiliated to the internet if you accept the bare admission permission and bounded software). phpPgAdmin is a web-based administering tool that allows querying abstracts stored on PostgreSQL database servers.
There are abounding added client applications, such as pgAdmin that acquiesce queries on abstracts stored on PostgreSQL (and added relational database engines such as Oracle). Some of these accommodate added elaborate SQL-based graphical interfaces to relational database engines, including SQuirreL, an accessible source, java-based accepted SQL client that is accessible at http://www.squirrelsql.org and can run on Macs.
However, to get adequate with the basics of SQL queries and relational thinking, we will alpha with our browser-based interface to PostgreSQL.
Since best of you are absurd to be accustomed with PostgreSQL, we spell out some of the tips and tricks for appliance the appliance and aing to it from your browser.
(A) Afterwards you are logged in to one of the lab machines, accessible your adopted web browser and go to http://cronpgsql.mit.edu/phppgadmin. Bang on the PostgreSQL server and you will be prompted to ample in a username and password. During the aboriginal class, you are activity to use a bedfellow account—user name “sqlguest”. The countersign will be accustomed by the adviser in class. During the aboriginal lab, we will accumulated your MIT advice in order to actualize a claimed PostgreSQL annual for you.
In consecutive labs you will use your own annual to admission the chic databases. You will additionally be able to admission PostgreSQL tables from a browser on your machines or from pgAdmin III, a PostgreSQL administering apparatus that allows the user to actualize databases and administer administer users and tables, and their attributes.
(B) The interface of PostgreSQL on a web browser via phpPgAdmin looks like the afterward (In this case we are appliance Mozilla Firefox)
(C) Cross to “toyparcels” on the annual that appears on the larboard ancillary of your browser. This is the database breadth our MS-Access Tables are amid in PostgreSQL. Accessible Schemas, afresh accessible and bang on Tables and you will see the name of all seven tables. Bang on “Browse” to attending at each of them.
At this point, you accept all the admission in place. You alone charge to accessible the affair apparatus by beat on “SQL” on the top-left bend of your browser. Once open, accomplish abiding the Database is set to “toyparcels” and Action is set to “public” (there are added schemas that acquiesce us to accumulate tables, sequences, etc. protected, but this time we are alone appliance tables that are public).
Now let’s use our small, academic bindle and acreage tax database to get a feel for how we can use phpPgAdmin to run simple queries on PostgreSQL. Elsewhere on the chic advice pages, we call this sample bindle database and the basal anatomy of the SELECT command. Blazon in some simple queries, or you can use cut-and-paste to grab pieces of queries apparent in the table below. You will apparently acquisition it accessible to edit the queries in a abstracted window with a argument editor such as ‘Notepad’. Back you are accomplished alteration a query, you can run it by acid and pasting the argument into the SQL window. Abounding servers crave that anniversary anniversary SQL account ends with a semi-colon ‘;’ afore acute the ‘Enter’ key, but this is not appropriate for PostgreSQL (although it is advised). Afresh bang assassinate and the aftereffect table will arise on your browser’s window.
Try out anniversary of the afterward SQL examples of SELECT statements:
– Do you accept what anniversary query is doing?
– Does the SQL syntax accomplish sense?
[In accession to the select…from…where structure, agenda the use of wildcards and the analysis of missing values, arithmetic expressions, accumulated functions such as min(tax) and count(*) ]
The simplest affair advertisement the TAX table
SELECT * FROM tax;
A query with an announcement and a cavalcade alias
SELECT parcelid, (landval bldval) AS tot_val, tax FROM tax;
A simple affair that aggregates (groups) over a accomplished table
SELECT COUNT(*), MIN(tax), MAX(tax), AVG(tax) FROM tax;
This archetype uses a accurate cord in the SELECT list
SELECT parcelid, ‘Total prop amount is’, (landval bldval) as tax FROM tax;
A simple affair appliance the “IS NULL” syntax to annual alone those accoutrements with at atomic 20,000 sq. ft. and no missing value
SELECT * FROM parcels WHERE sqft >= 20000 OR sqft IS NULL;
Compare the after-effects of the affair 5 with affair 6. Why are they different?
SELECT * FROM parcels WHERE sqft >= 20000 OR sqft = NULL;
A query to acquisition ethics aural a assertive range
SELECT * FROM parcels WHERE sqft >= 10000 AND sqft <= 100000;
Another way of autograph the affair aloft appliance the– “BETWEEN” keyword
SELECT * FROM parcels WHERE sqft BETWEEN 10000 AND 100000;
A simple accompany amid PARCELS and FIRES. Agenda that only those accoutrements which had fires are listed.
SELECT p.*, f.estloss FROM accoutrements p, fires f WHERE p.parcelid = f.parcelid;
A slight aberration of affair 9.
SELECT p.parcelid, p.sqft, p.landuse, f.estloss FROM accoutrements p, fires f WHERE p.parcelid = f.parcelidORDER BY f.estloss;
We cannot save or book the SQL account and the affair aftereffect directly on phpPgAdmin. However, you can archetype your SQL statements and paste them into a argument editor such as Notepad, and afresh book from there.
‘Print’ out the SQL statements and the affair after-effects for Affair 3, 7 and 10 in the aloft table of queries. Actually, there is no charge to generate printed adamantine copy. All the contest will be submitted electronically to the chic appointment locker on Stellar. CRON machines accept a ‘printer’ alleged ‘Adobe PDF’ that, instead of press a document, saves it in PDF architecture aural a binder of your choosing. All Athena clusters accept admission to concrete printers via a arrangement alleged ‘Pharos’ that controls the acquisition of your printout. See this website: http://kb.mit.edu/confluence/display/istcontrib/Pharos Accessible Apprentice Press at MIT for added advice about how to book from Athena machines. See this website: http://cronlasso.mit.edu/cron/p.lasso?t=4:2:0 for added advice about press from CRON machines. Basically, afterwards ‘printing’ you charge absolution a book job for press on a accurate machine.
At the moment, there are no printing accessories in or a our lab in Room W31-301. If you ambition to save files for press afterwards in CRON or some added facility, be abiding to archetype the files to your Athena locker afore abrogation the lab. In any event, there is no charge to book annihilation today. CRON additionally provides ample architecture acute capabilities.
Your file(s) absolute your lab exercise #1 can be uploaded to Arch afterwards this anniversary back we accept provided admission to you to the chic appointment about-face in breadth on Stellar.
This aboriginal lab exercise is intended to accustom you with the accretion ambiance acclimated for the class and with the accoutrement accessible to move abstracts amid assorted desktop applications and database engines. Don’t anguish if you are not accustomed abundant at the alpha with the assorted accoutrement and the steps bare to accomplish the connections. We will altercate them a bit in today’s lab and afresh in consecutive lectures and labs.
You should about-face in PDF copies of:
– The three ‘printouts’ declared in Allotment II aloft from
– The map you created in the ArcGIS analysis contest (if you haven’t already taken 11.205, 11.520 or 11.188).
Make abiding that your name, MIT email abode and the date are on the submission. If you ambition to include the PDFs as allotment of a Word certificate that you abide as a single file, that is accept too. If you ambition to abide appointment appliance some added book format, amuse analysis with the Adviser apropos the accurate format. The lab appointment should be uploaded to the 11.521 Arch website (https://stellar.mit.edu/S/course/11/sp18/11.521) by the alpha of aing week’s lab exercise at 4pm Tuesday, February 13, 2018. (Note, you may not be able to admission the arch armpit until a few days from now back you accept been added to the chic list.)
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