2026-09-19T19:49:30Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/97784 2023-07-11 col_2142_5131 col_2142_10761 com_2142_5130 com_2142_10755 com_2142_234

Han, Jiawei Zhang, Keyang 2017-08-10T20:33:25Z 2017-08-10T20:33:25Z 2019-08-11T09:15:39Z 2017-04-27 2017-05 With the ever-increasing urbanization process, systematically modeling people's activities in the urban space is being recognized as a crucial socioeconomic task. This task was nearly impossible years ago due to the lack of reliable data sources, yet the emergence of geo-tagged social media (GTSM) data sheds new light on it. Recently, there have been fruitful studies on discovering geographical topics from GTSM data. However, their high computational costs and strong distributional assumptions about the latent topics hinder them from fully unleashing the power of GTSM. To bridge the gap, we present CrossMap, a novel cross-modal representation learning method that uncovers urban dynamics with massive GTSM data. After extracting activity-related tweets by measuring the dispersion degree of each keyword, CrossMap first employs an accelerated mode seeking procedure on all the extracted activity-related tweets to detect the spatiotemporal hotspots underlying people's activities. Those detected hotspots not only address spatiotemporal variations, but also largely alleviate the data sparsity of the GTSM data. With the detected hotspots, CrossMap then jointly embeds all spatial, temporal, and textual units into the same space using two different strategies: one is reconstruction-based and the other is graph-based. Both strategies capture the correlations among the units by encoding their co-occurrence and neighborhood relationships, and learn low-dimensional representations to preserve such correlations. Our experiments show that CrossMap not only significantly outperforms state-of-the-art methods for activity recovery, but also greatly benefits downstream applications like activity classification. Further, CrossMap is capable of processing millions of GTSM records within minutes, making it suitable for monitoring large-scale GTSM streams in practice. We also further extend our model in two ways. Firstly, we adopt a novel semi-supervised learning paradigm that leverages the activity category information to guide the embedding learning process to generate higher quality embeddings. Secondly, to overcome the existing models' incapability of dynamically accommodating the latest information in the GTSM stream, we propose a method that processes continuous GTSM streams and obtains recency-aware urban activity models on the fly, in order to reflect up-to-date urban activities. Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2019-05-01 The student, Keyang Zhang, accepted the attached license on 2017-04-25 at 16:00. The student, Keyang Zhang, submitted this Thesis for approval on 2017-04-25 at 16:09. This Thesis was approved for publication on 2017-04-27 at 16:44. DSpace SAF Submission Ingestion Package generated from Vireo submission #11059 on 2017-08-10 at 15:07:03 Made available in DSpace on 2017-08-10T20:33:25Z (GMT). No. of bitstreams: 2 ZHANG-THESIS-2017.pdf: 8835639 bytes, checksum: b702ab5fcd31a3ca65949cc49f8b6612 (MD5) LICENSE.txt: 4209 bytes, checksum: 30660b28120287f975fcbe84e71abc36 (MD5) Previous issue date: 2017-04-27 Embargo set by: Colleen Fallaw for item 102837 Lift date: 2019-08-10T21:27:21Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system U of I Only Restriction Lifted for Item 102837 on 2019-08-11T09:15:39Z. application/pdf http://hdl.handle.net/2142/97784 en Copyright 2017 Keyang Zhang Urban dynamics Activity modeling Representation learning Embedding Uncovering urban dynamics via cross-modal representation learning text text Computer Science Computer Science University of Illinois at Urbana-Champaign Thesis M.S.